Don't try to push the docker container on a PR as that will
fail for PRs that aren't from project members

actions-rs is no longer maintained, switch over to dtolnay/rust-toolchain
instead which is. While there also ensure the various checks also check
all targets/features as applicable

For the rust toolchain aim for a specific version so CI doesn't start
failing over time. For the version also aim for the version of rustc in
debian unstable to ensure things can build with that version of the
compiler

To allow catching newer clippy lints also run clippy from the latest
stable rust toolchain. This check is allowed to fail so CI doesn't start
failing due to newer lints being introduced.

Check the build still works when actually using the (direct) minimal
dependencies. For now this needs a nightly rust

For merge queue's to work the CI has to run on the `merge_group` event.
Also ignore pushes to the merge queue branches to avoid running CI twice

Update the required crate versions as needed to ensure the build
succeeds with direct minimal versions as well as some smaller updates
for new crate versions