Remove explicit OS/libc versions in CI workflows

Two things: * The defaults are already the minimum version supported by the Zig standard library abstractions. * Our choice of supporting glibc all the way back to 2.17 is unsupported by the Zig standard library. So just avoid specifying versions altogether. This might require some changes done in https://github.com/ziglang/zig/pull/20909 so will be done with Zig 0.14.0.