concurrent map writes in integration-tests

[mzihlmann]

Actual behavior
We now run all integration tests in parallel, occasionally they crash with a concurrency issue:

https://github.com/osscontainertools/kaniko/actions/runs/19255094029/job/55048032841?pr=372

specifically this access here https://github.com/osscontainertools/kaniko/blob/deprecated-compression/integration/images.go#L427

Expected behavior
maybe mutex lock access or find some other architecture that doesn't require a shared resource between the tests.

[mzihlmann]

its just there as a memoization wrapper around BuildImageWithContext. not sure that is actually any helpful tbh. as I would expect integration tests to anyways only build an image a single time, unless it is explicitly wished for like when testing caching etc.

[mzihlmann]

ok the same files are called from TestLayers and TestRun for example, they build the same images but they use different grading mechanisms. Maybe we should just combine them into one test? In CI they are tested in parallel so the memoization only affects local usage anyways.