Dump layer map json in test_gc_feedback.py

[arpad-m]

The layer map json is an interesting file for that test, so dump it to make debugging easier.

[github-actions]

2730 tests run: 2599 passed, 0 failed, 131 skipped (full report)

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Flaky tests (2)

Postgres 16

• test_vm_bit_clear_on_heap_lock: debug

Postgres 14

• test_wal_restore_http[True]: debug

Code coverage* (full report)

• functions: 28.3% (7133 of 25199 functions)
• lines: 46.9% (43726 of 93295 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
70e1ccd at 2024-03-20T17:36:06.010Z :recycle:}