sigstore: Tweak method signature

underscore prefix was used to avoid a too-many-locals warning:
Workaround that otherwise to make the method signature match the
parent class.

securesystemslib/signer/_sigstore_signer.py

@@ -141,7 +141,7 @@ def from_priv_key_uri(
         cls,
         priv_key_uri: str,
         public_key: Key,
-        _secrets_handler: Optional[SecretsHandler] = None,
+        secrets_handler: Optional[SecretsHandler] = None,
     ) -> "SigstoreSigner":
         # pylint: disable=import-outside-toplevel
         try:
@@ -163,8 +163,7 @@ def from_priv_key_uri(
         if not ambient:
             # TODO: Restrict oauth flow to use identity/issuer from public_key
             # TODO: Use secrets_handler for identity_token() secret arg
-            issuer = Issuer.production()
-            token = issuer.identity_token()
+            token = Issuer.production().identity_token()
         else:
             credential = detect_credential()
             if not credential: