[chore](build) Reduce redundant Actions on branch-4.1

[hello-stephen]

Background

Release-branch GitHub Actions are frequently queued, including redundant post-merge runs and a thirdparty change detector on unrelated PRs.

Changes

• Remove the duplicate Check Large File push trigger; keep pull_request_target.
• Remove the legacy Need_2_Approval workflow. The branch's Code Owner approval policy remains the merge gate.
• Start Build Third Party Libraries on PRs only when its relevant inputs change. Keep workflow_dispatch and issue_comment triggers.

Scope note

Code Checks is unchanged; its push trigger optimization is deferred for separate review.

External Regression's regression-test/pipeline/external/conf/fe.conf is excluded from both the PR entry filter and the old focused test filter. A change to that file alone will no longer trigger Thirdparty Script Test or its ADBC JNI assertion. The assertion still runs when a thirdparty-related change triggers the script test; this PR does not move it to another workflow.

Validation

• actionlint passed for all edited workflow files (excluding pre-existing inline shellcheck and old-runner warnings).
• git diff --check passed.
• No required GitHub check on branch-4.1 is path-filtered by this PR.

No TeamCity pipeline or branch governance configuration is changed.

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[mbien]

@hello-stephen also: consider using ubuntu-slim for short running actions like

doris/.github/workflows/approve-label-trigger.yml

Lines 25 to 28 in 28577df

	runs-on: ubuntu-latest
	steps:
	- name: "Do nothing. Only trigger corresponding workflow_run event"
	run: echo

it would come with less overhead since it runs in a container.