Pull GCC <=11 from another PPA in CI build.

[adamshapiro0]

Fixes

• Fixed failing CI apt installs for earlier GCC versions

[bhers4]

Looks good to me! Hit the same problem last night and an alternative solution I found was using apt-get. This worked as well: sudo apt-get install -y --fix-missing gcc-${{ matrix.version }} g++-${{ matrix.version }}

[adamshapiro0]

Huh I'm surprised --fix-missing worked. That tells apt to ignore the 404s and continue installing any other packages you asked for, but when it finishes gcc-11 still won't be installed (since it had a 404).