replace set-env with github env file workflow (#6945)

Suggested workaround for security vulnerability listed at,
GHSA-mfwh-5m23-j46w

This error can be spotted in the logs currently,
The `set-env` command is deprecated and will be disabled on November 16th. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

Author: vimanyu

scripts/generate_access_token.sh

@@ -69,7 +69,7 @@ else
     scripts/decrypt_GHA_SECRET.sh $SERVICE_ACCOUNT ~/.credentials/$SERVICE_ACCOUNT_FILE "$plist_secret"
 fi
 
-echo "::set-env name=GOOGLE_APPLICATION_CREDENTIALS::${HOME}/.credentials/${SERVICE_ACCOUNT_FILE}"
+echo "GOOGLE_APPLICATION_CREDENTIALS=${HOME}/.credentials/${SERVICE_ACCOUNT_FILE}" >> $GITHUB_ENV
 export GOOGLE_APPLICATION_CREDENTIALS="${HOME}/.credentials/${SERVICE_ACCOUNT_FILE}"
 
 # Clone Google's Swift Auth Client Library and use it to generate a token.