Interactively approving approval tests fails with uv

[koebi]

The python standalone provided by uv does not provide Tk bindings, which is the default visualizer for approval tests.
See https://github.com/matplotlib/matplotlib/pull/29752/files and astral-sh/uv#6893 for details.

We should check whether some other backends are available (e.g. PyCharm, any graphical diff tool, …) and fall back to them, or in the worst case explain to the user which two images they should look at.