use older Ubuntu for Linux build for "more compatible binaries"

[ptahmose]

Description

• Use an older Ubuntu-version for the runner in order to have the binaries being linked to an older C/C++ runtime. This should increase compatibility with older distros.
• Fix an error in the Github-actions-yaml (which had the funny effect of using the wrong caches I think).

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Locally - I tested the resulting Linux-binary on a Debian-bullseye-box, and it worked fine. The current binary (built with 'ubuntu-latest') did not work.

Checklist:

• I followed the Contributing Guidelines.
• I did a self-review.
• I commented my code, particularly in hard-to-understand areas.
• I updated the documentation.
• I updated the version of czicompress following the README (Versioning) depending on the type of change
  • Bug fix -> PATCH
  • New feature -> MINOR
  • Breaking change -> MAJOR
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.