fix(gcp): reduce scope of GCP App Default Creds script to template

templates/gitlab-ci-python-gcp.yml

@@ -19,8 +19,7 @@ variables:
   GCP_OIDC_ACCOUNT: $[[ inputs.gcp-oidc-account ]]
   GCP_OIDC_PROVIDER: $[[ inputs.gcp-oidc-provider ]]
 
-.gcp-provider-auth:
-  before_script:
+.python-gcp-adc:
   - set -e
   - echo -e "[\\e[1;94mINFO\\e[0m] Installing GCP authentication with env GOOGLE_APPLICATION_CREDENTIALS file"
   - echo $GCP_JWT > "$CI_BUILDS_DIR/.auth_token.jwt"
@@ -39,21 +38,19 @@ variables:
     EOF
   - export GOOGLE_APPLICATION_CREDENTIALS="$CI_BUILDS_DIR/google_application_credentials.json"
 
-
 .python-base:
   image: $PYTHON_IMAGE
   services:
     - name: "$TBC_TRACKING_IMAGE"
       command: ["--service", "python", "7.8.1"]
+  id_tokens:
+    GCP_JWT:
+      aud: "$GCP_OIDC_AUD"
   variables:
     GCP_JWT: $GCP_JWT
   before_script:
-    - !reference [.gcp-provider-auth, before_script]
     - !reference [.python-scripts]
+    - !reference [.python-gcp-adc]
     - install_ca_certs "${CUSTOM_CA_CERTS:-$DEFAULT_CA_CERTS}"
     - cd ${PYTHON_PROJECT_DIR}
     - guess_build_system
-
-  id_tokens:
-    GCP_JWT:
-      aud: "$GCP_OIDC_AUD"