chore: update minimum version of gax (#6935)

Author: bshaffer

composer.json

@@ -6,7 +6,7 @@
     "require": {
         "php": ">=7.4",
         "google/cloud-core": "^1.52.7",
-        "google/gax": "^1.24.0"
+        "google/gax": "^1.26.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^9.0",