Skip integration tests or other expensive jobs when unnecessary

[AlanGreene]

Integration tests are currently run on all PRs, even if the files modified don't impact the tests.

For example, a PR that only modifies docs or other workflow definitions wouldn't impact the outcome of the integration tests, but they are still run and required to pass for the PR to be merged.

This can be problematic in case of flaky tests, where PRs that could otherwise be merged are blocked and numerous retries are required, wasting both time and resources.

Recent example: https://github.com/tektoncd/pipeline/issues/9052

Action:

Review integration tests across the projects and apply filters / exclusions so they only run when necessary.

[AlanGreene]

Related https://github.com/tektoncd/pipeline/pull/8768#issuecomment-3364765090 Using paths-ignore on the workflow may not be suitable