Fix dependencies of overlay_images tool

[kostrykin]

Previous versions of the tool required numpy 1.20, that does not offer the numpy.typing package.

One of the other dependencies of the tool is scikit-image, which in turn requires pillow. When testing without containerization (i.e. without the --biocontainers switch), the tests failed, because seemingly a newer version of pillow was installed (10.4.0, compared to testing with containerization). However, pillow 10.4.0 requires the numpy.typing package, that isn't there with numpy 1.20:

AttributeError: module 'numpy.typing' has no attribute 'NDArray'

The same issue could be reproduced by running a local Galaxy instance without containerization (which is very much the procedure suggested in https://galaxyproject.org/admin/get-galaxy).

To fix these issues, this PR bumps numpy to 1.21 (which includes the numpy.typing package) and pins pillow to 10.4.0 (to prevent similar issues in the future).

Could be related to #121.

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