[v10.3.x] ImagePullSecrets: Add GAR secret to image_pull_secret in .drone.yml (#80919)

`ImagePullSecrets`: Add `GAR` secret to `image_pull_secret` in `.drone.yml` (#80912)

* Add GAR secret to image_pull_secret

* Fix starlark fmt

(cherry picked from commit 65104a7efa)

scripts/drone/vault.star

@@ -1,7 +1,8 @@
 """
 This module returns functions for generating Drone secrets fetched from Vault.
 """
-pull_secret = "dockerconfigjson"
+gcr_pull_secret = "gcr"
+gar_pull_secret = "gar"
 drone_token = "drone_token"
 prerelease_bucket = "prerelease_bucket"
 gcp_upload_artifacts_key = "gcp_upload_artifacts_key"
@@ -43,7 +44,8 @@ def secrets():
         vault_secret(gcp_grafanauploads, "infra/data/ci/grafana-release-eng/grafanauploads", "credentials.json"),
         vault_secret(gcp_grafanauploads_base64, "infra/data/ci/grafana-release-eng/grafanauploads", "credentials_base64"),
         vault_secret("grafana_api_key", "infra/data/ci/grafana-release-eng/grafanacom", "api_key"),
-        vault_secret(pull_secret, "secret/data/common/gcr", ".dockerconfigjson"),
+        vault_secret(gcr_pull_secret, "secret/data/common/gcr", ".dockerconfigjson"),
+        vault_secret(gar_pull_secret, "secret/data/common/gar", ".dockerconfigjson"),
         vault_secret("github_token", "infra/data/ci/github/grafanabot", "pat"),
         vault_secret(drone_token, "infra/data/ci/drone", "machine-user-token"),
         vault_secret(prerelease_bucket, "infra/data/ci/grafana/prerelease", "bucket"),