Support disabling bazel tests in release_ruleset.yaml

I'm looking at adopting attestations for the Apple rulesets (apple_support, rules_swift, rules_apple), and I noticed that the `Test` step of `release_ruleset.yaml` is non-optional. I believe we'd prefer not to run this, for two reasons:

- The vast majority of our tests require a macOS environment, and the workflow is configured to run on ubuntu-latest
- There are challenges with the tests running on GitHub Actions' macOS runners out-of-the-box that make a seamless transition from bazelci to GHA difficult to make a requirement.
- Testing rules_apple in particular takes a long time, and we wouldn't want this to block cutting a release

I was going to try hacking together a `bazel_test_command` input that tested nothing special to get us past this, but I would prefer we have a way to disable this in the workflow_call altogether. What do you think?

Read release_ruleset.yaml, focusing on the Test step and its workflow_call inputs. Determine how the workflow currently invokes Bazel tests and make that step optional for callers; done means a release can disable testing while the existing test behavior remains available.

Written by the indexing model from the issue text.