[Rust 1.80 from July 25th 2024] points out that `armv7` is not a known,
valid value for the `target_arch` cfg variable.  This is confirmed by
the docs not listing it either:
https://doc.rust-lang.org/reference/conditional-compilation.html#target_arch

Hence drop this entirely, and rely purely on `target_arch = "arm"`.

[Rust 1.80 from July 25th 2024]: https://blog.rust-lang.org/2024/07/25/Rust-1.80.0.html

…test`

Some code copied from the NDK carried over the respective `feature`
`cfg` guards, without ever adding the feature to the `[features]` list
in `Cargo.toml`.  Now that Rust detects these mishaps, we can fix it
by removing `test` (bindings don't seem to be run-tested) and reexpose
`ConfigurationRef::screen_round()` which was behind a previously
unsettable `feature = "api-level-30"`.

Also remove `unsafe impl Send/Sync for ConfigurationRef` since the
upstream `ndk` already declares `Configuration` to be `Send` and `Sync`,
and `RwLock` and `Arc` carry that through.

…ndSync` and unwritten `redraw_needed` field

The `actions-rs` containers haven't been maintained and updated for
years and don't need to: GitHub's actions environment already comes
fully loaded with a complete `stable` Rust installation with the
standard tools (in this case `rustfmt`).  Remove the remaining toolchain
setup (which was already replaced with `hecrj/setup-rust-action`
elsewhere) to get rid of ancient Node 12 deprecation warnings.

…heck

Use `-Zminimal-versions` in our MSRV check.  This not only ensures
our minimum version bounds are actually solid and tested (even if
they may be a bit conservative at times, i.e. we could allow older
versions except for the crates that are bumped in this patch which were
explicitly build-tested), it also allows us to use this as a base for
the MSRV test, and preempt us from failing it whenever a (transitive!)
dependency bumps its MSRV beyond ours in a *semver-compatible* release.