ci(functions): update tests to use labeled on pull_request trigger

[grayside]

Description

This change applies the new triggering pattern defined in #3747 to the workflows with filenames prefixed with functions*.

Looking at the checks, there are some big numbers:

• These workflows are running on pull_request for a number of samples
• flakybot jobs are skipped in PRs
• remove-label jobs are skipped when a label isn't used to trigger

In the middle of iterating this PR, I tested using the label trigger. As expected, this double-triggered, because it activated both the pull_request trigger in this PR and the pull_request_target trigger merged to main.

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

[iennae]

LGTM; Thank you!