crane: Gitlab runner issue because of new busybox image

[antonvdl]

Describe the bug

Since #1638 there is an issue with gitlab runners.
Gitlab runner uses BashDetectShellScript see bash.go for the script.

This script detects a /bin/bash file in the Chainguard image, but the /bin/bash is not working
/bin/bash is a symlink to /bin/busybox; which automatically runs /bin/busybox bash.
Running /bin/bash or /bin/busybox bash will result in an error.

To Reproduce

/bin $ /bin/bash
bash: applet not found

/bin $ /bin/busybox bash
bash: applet not found

Expected behavior

/bin $ /bin/bash
sh: /bin/bash: not found

[github-actions]

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