Revert "redhat: gating.yaml: drop unstable test"

JIRA: INTERNAL
Upstream Status: RHEL only

Reinstate s1-gcp-ci.brew-build.tier1.functional test, owners
said it's stable now.

This reverts commit 6a12185.

Signed-off-by: Jan Stancek <jstancek@redhat.com>

Author: jstancek

redhat/scripts/gating/gating.yaml

@@ -23,3 +23,4 @@ rules:
   - !PassingTestCaseRule {test_case_name: s1-aws-ci_aarch64.brew-build.tier1.functional}
   - !PassingTestCaseRule {test_case_name: s1-azure-ci_x86_64.brew-build.tier1.functional}
   - !PassingTestCaseRule {test_case_name: s1-azure-ci_aarch64.brew-build.tier1.functional}
+  - !PassingTestCaseRule {test_case_name: s1-gcp-ci.brew-build.tier1.functional}