[3.12] gh-113858: GH Actions: Make ccache smaller (GH-113859, GH-113945) (GH-114082)

This backports 3 PRs:

- https://github.com/python/cpython/pull/113859

  Only save ccache on pushes

- https://github.com/python/cpython/pull/113945

  Cut down ccache size

  - Only save the ccache in the main reusable builds, not on builds that
    don't use special build options:
      - Generated files check
    - OpenSSL tests
    - Hypothesis tests
  - Halve the max cache size, to 200M

- https://github.com/python/cpython/pull/114113

  Fixup for the above

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>