Flaky unit test: `test_load_mappings_cache`

[jayaddison]

Describe the bug

There seems to be an flaky/intermittent test failure for test_load_mappings_cache; this appeared as a failure in a recent GitHub Actions CI unit test run for v8.2.0 of Sphinx.

The test involves building an application, performing some cleanup, and then asserting that an InventoryAdapter constructed on the results contains an expected Intersphinx cache item as configured during the app build -- but during the failure observed, the cache entry was not found.

How to Reproduce

TBD; the failure can currently be found in the build logs for this GitHub Actions CI job: https://github.com/sphinx-doc/sphinx/actions/runs/13402480912/job/37436044034

Environment Information

Platform:              linux; ([Linux-6.8.0-1021-azure](https://github.com/actions/runner-images/blob/ubuntu24/20250209.1/images/ubuntu/Ubuntu2404-Readme.md))
Python version:        3.13.2 (main, Feb  5 2025, 03:27:26) [GCC 13.3.0]
Python implementation: CPython
Sphinx version:        8.2.0
Docutils version:      0.20.1
Jinja2 version:        3.1.5
Pygments version:      2.19.1

Sphinx extensions

N/A

Additional context

No response

[jayaddison]

Re-occurence (2025-05-12): https://github.com/sphinx-doc/sphinx/actions/runs/14978076771/job/42075345604?pr=13538#step:8:2456

[jayaddison]

Re-occurence (2025-05-12): https://github.com/sphinx-doc/sphinx/actions/runs/14978076771/job/42075345604?pr=13538#step:8:2456

Plus one more (also 2025-05-12): https://github.com/sphinx-doc/sphinx/actions/runs/14978473927/job/42076652013?pr=13538#step:8:2456