ci: Update a-c workflows for labeled on pull_request trigger

[grayside]

Description

Scoped to Samples workflows with file names starting with a-c.

Implementation of #3747, sibling of #3748. App Engine updates were handled in #3749.

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Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[grayside]

• Asset test is failing on a test concurrency bug, it's failing on "resource already exists". Retry of the pull_request trigger succeeded.
• Compute is failing on an unrecognized image reference:

The resource 'projects/debian-cloud/global/images/family/debian-10' was not found

I've recorded these for follow-up bug filing, neither is in scope for this PR.