fix(log): preserve dict of rest async response headers (#2288)

Author: vchudnov-g

packages/gapic-generator/gapic/templates/%namespace/%name_%version/%sub/services/%service/transports/rest_asyncio.py.j2

@@ -228,7 +228,7 @@ class Async{{service.name}}RestTransport(_Base{{ service.name }}RestTransport):
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(

packages/gapic-generator/tests/integration/goldens/redis/google/cloud/redis_v1/services/cloud_redis/transports/rest_asyncio.py

@@ -813,7 +813,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -938,7 +938,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -1066,7 +1066,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -1194,7 +1194,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -1316,7 +1316,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -1438,7 +1438,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -1566,7 +1566,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -1690,7 +1690,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -1818,7 +1818,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -1946,7 +1946,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(
@@ -2074,7 +2074,7 @@ async def __call__(self,
                     response_payload = None
                 http_response = {
                     "payload": response_payload,
-                    "headers":  str(dict(response.headers)),
+                    "headers":  dict(response.headers),
                     "status": "OK", # need to obtain this properly
                 }
                 _LOGGER.debug(