planner/test: make reports replay deterministic with repo testdata

[hawkingrei]

What problem does this PR solve?

Issue Number: close #66107

Problem Summary:
The reports replay test currently depends on local ad-hoc reports/ files and can become a no-op in CI/dev environments.

What changed and how does it work?

• Add deterministic reports replay test: pkg/planner/core/casetest/join/reports_test.go.
• Add repository-managed testdata under pkg/planner/core/casetest/join/testdata/reports/case_65454/.
• Update pkg/planner/core/casetest/join/BUILD.bazel to include reports_test.go.
• The test now reads testdata/reports/case_*/summary.json instead of external local reports/ directories.

Dependency note:

• This PR contains a regression repro case and is expected to be merged after the join-reorder fix PR (#66116).

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Manual test scripts:

• go test -run TestReportsCantFindColumn --tags=intest ./pkg/planner/core/casetest/join -count=1

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[ti-chi-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[ti-chi-bot]

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[tiprow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[hawkingrei]

Superseded by #66116. Per reviewer preference, test changes are folded into the main fix PR instead of staying in a separate test-only PR.