Test mkcw-convert flakes a lot in CI

[flouthoc]

For some reason test mkcw-convert flakes a lot in CI.

• https://cirrus-ci.com/task/6539966114693120?logs=integration_test#L940

Opening this issue to keep track of this flake.

[Luap99]

You need to copy paste the error output, the CI logs will be deleted after 90 days AFAICT.
Future readers will need to know what this is about:

[+1244s] not ok 687 mkcw-convert
[+1244s] # (from function `mkcw_check_image' in file ./mkcw.bats, line 46,
[+1244s] #  in test file ./mkcw.bats, line 71)
[+1244s] #   `mkcw_check_image busybox-cw ${TEST_SCRATCH_DIR}/randomfile1:in-a-subdir/rnd1' failed with status 5
[+1244s] # /var/tmp/go/src/github.com/containers/buildah/tests /var/tmp/go/src/github.com/containers/buildah/tests
[+1244s] # # [checking for: docker.io/library/busybox]
[+1244s] # # [restoring from cache: /var/tmp/bats-run-fWohMM/suite/buildah-image-cache / docker.io/library/busybox]
[+1244s] # Getting image source signatures
[+1244s] # Copying blob sha256:9758c28807f21c13d05c704821fdd56c0b9574912f9b916c65e1df3e6b8bc572
[+1244s] # Copying config sha256:f0b02e9d092d905d0d87a8455a1ae3e9bb47b4aa3dc125125ca5cd10d6441c9f
[+1244s] # Writing manifest to image destination
[+1244s] # # [checking for: quay.io/libpod/testimage:20221018]
[+1244s] # # [copy docker://quay.io/libpod/testimage:20221018 dir:/var/tmp/bats-run-fWohMM/suite/buildah-image-cache/quay.io-libpod-testimage-20221018-]
[+1244s] # Getting image source signatures
[+1244s] # Copying blob sha256:578f06cc66c59303d36e0c83b8c7fd9b2da35cca97118700cb4a373677c01dca
[+1244s] # Copying blob sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
[+1244s] # Copying config sha256:f5a99120db6452661930a1db3bf7390eec9b963f5f62c068fa32dc1d550afad3
[+1244s] # Writing manifest to image destination
[+1244s] # # [copy dir:/var/tmp/bats-run-fWohMM/suite/buildah-image-cache/quay.io-libpod-testimage-20221018- containers-storage:quay.io/libpod/testimage:20221018]
[+1244s] # Getting image source signatures
[+1244s] # Copying blob sha256:578f06cc66c59303d36e0c83b8c7fd9b2da35cca97118700cb4a373677c01dca
[+1244s] # Copying blob sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
[+1244s] # Copying config sha256:f5a99120db6452661930a1db3bf7390eec9b963f5f62c068fa32dc1d550afad3
[+1244s] # Writing manifest to image destination
[+1244s] # # /var/tmp/go/src/github.com/containers/buildah/tests/./../bin/buildah mkcw --ignore-attestation-errors --type snp --passphrase=mkcw-convert --add-file /var/tmp/buildah_tests.snbyei/randomfile1:/in-a-subdir/rnd1 busybox busybox-cw
[+1244s] # 7c6225ca9953f977d57f9f6d9bdc02257b234ff91036fbe08c3623195bd56626
[+1244s] # # /var/tmp/go/src/github.com/containers/buildah/tests/./../bin/buildah from busybox-cw
[+1244s] # busybox-cw-working-container
[+1244s] # # /var/tmp/go/src/github.com/containers/buildah/tests/./../bin/buildah mount busybox-cw-working-container
[+1244s] # /var/tmp/buildah_tests.snbyei/root/overlay/41757d4949603f74dab68c71987c4df0e9dde7592ab372f9ea565042cc475c98/merged
[+1244s] # Device 44afc014-5d72-4d6e-bea6-bc9666bcff9a is still in use.
[+1244s] # umount: /var/tmp/buildah_tests.snbyei/root/overlay/41757d4949603f74dab68c71987c4df0e9dde7592ab372f9ea565042cc475c98/merged: target is busy.
[+1244s] # umount: /var/tmp/buildah_tests.snbyei/root/overlay: target is busy.
[+1244s] # rm: cannot remove '/var/tmp/buildah_tests.snbyei/root/overlay/41757d4949603f74dab68c71987c4df0e9dde7592ab372f9ea565042cc475c98/merged': Device or resource busy
[+1244s] # /var/tmp/go/src/github.com/containers/buildah/tests

Also as you can see here /var/tmp/buildah_tests.snbyei is used so I don't think your tmpfs PR does anything until you configure tests to use /tmp.