CI: Combine MSRV-check with -Zminimal-versions build

[MarijnS95]

Sometimes dependency crates bump their MSRV beyond our MSRV in a patch release, and fail our CI in subsequent versions. Instead of downgrading independent crates in CI every time this issue arises, combine it with our already-existing -Zminimal-versions check. Instead of running this check on nightly, we only use that toolchain to generate a Cargo.lock and subsequently check the code on our MSRV toolchain.

[MarijnS95]

https://github.com/Smithay/drm-rs/actions/runs/11681253865/job/32525926098?pr=212

error[E0433]: failed to resolve: use of undeclared crate or module `syntax`
Error:  --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/regex-1.5.0/src/literal/mod.rs:9:9
  |
9 |     use syntax::hir::literal::Literals;
  |         ^^^^^^ use of undeclared crate or module `syntax`

It's been a while since I last saw this one: rust-lang/regex#931. It's showing up now because the original MSRV check builds with --all-features, which we now combine with a -Zminimal-versions build as I outlined in rust-lang/regex#931 (comment). Bumping our minimum bindgen version to 0.69.3 which includes rust-lang/regex#931 should solve this. Otherwise we have to change our --all --all-features build?

[MarijnS95]

Note that the original -Zminimal-versions build wasn't building minimal versions at all. See a detailed breakdown at #211 (comment).

[Drakulix]

Superseeded by #211 & #227