chore: Split pipelines to run only integration tests with pull_request_trigger

[DanielSchiavini]

What I did

Moved the integration tests to a separate pipeline Merge the base branch into the PR for integration tests Move the other tests back to the pull_request trigger

How I did it

• merge_commit_sha is not available
• We need to manually merge the base branch.

How to verify it

After merging this PR, new PRs with pull_request_target should work on the merge commit. See the pipeline run at https://github.com/DanielSchiavini/titanoboa/pull/4

Description for the changelog

N/A

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