CI: Free up disk space for Android CI

[kateinoigakukun]

Let's see if the flaky CI will be improved

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I suspect the problem is actually due to low disk space. Looking at the recent Android CI failures (19877954893, 19877165089, 19868624244, and 19859198948), they are all preceded by an error when installing the Android SDK:

Warning: An error occurred while preparing SDK package Intel x86_64 Atom System Image: No space left on device.

You might want to try having the Android CI free some disk space at the beginning of the run, using either an action like free-disk-space-ubuntu or just by manually deleting some useless junk like /opt/hostedtoolcache/CodeQL and /usr/share/dotnet.

#231 (comment)