ci: pypi: use manylinux_2_28 consistently

[woodruffw]

Using auto causes us to default to exceptionally
old versions of glibc, along with containers that
struggle badly to build things like tree-sitter.

See: tree-sitter/tree-sitter#4186

See: tree-sitter/tree-sitter#4271

[woodruffw]

We're in a pickle here:

1. We can't switch with auto, since it selects an exceptionally old container with a version of GCC that doesn't play nicely by default with tree-sitter's build. I could probably hack around this, but it's not worth it just to support a small number of EOL manylinux tags.
2. We can't upgrade all the way to 2_28, since maturin-action appears to have trouble bootstrapping its toolchain with the system pip there: No module named pip for x86 manylinux_2_28 PyO3/maturin-action#249. I could work around that by disabling sccache, but I'd really prefer not to.

[woodruffw]

I'm declaring bankruptcy on making this work consistently, and limiting my scope of interest to the following platforms going forwards for wheel builds:

• macOS: ARM64 and AMD64
• Linux: musl with ARM64/Arm7/AMD64, glibc 2.28+ for ARM64/Arm7/AMD64. Some wheels may also be glibc 2.24+, but this will be dropped since 2.24 is pretty consistently EOL on distros.
• Windows: AMD64 and x86

Anything else might be supported again in the future, but will probably be contingent on a more reliable build setup + fewer pain points with our non-Rust dependencies (namely, ring and tree-sitter).