chore: fix test suite on macOS (#12780)

MacOS uses a very old version of bash where `"${FOO[@]}"` fails if `set
-u` is enabled and `FOO` is undefined. Newer versions of bash expand
this to zero arguments instead.

Also, `lint.py` used the shebang `#!/usr/bin/env python` instead of
`python3`, which fails on some systems.

In CI, all macos tests run on nscloud runners. Presumably, they have
installed newer versions of various software, hence this didn't break in
CI.