Our MSRV is used in a number of places:

• Doc comment in src/lib.rs
• .github/workflows/ci.yml
• tests/trybuild.rs (added in Make Unalign::into_inner const #60, which hasn't merged as of this writing)
• zerocopy-derive/tests/trybuild.rs

Since they all need to be updated manually, it's easy for them to get out of sync. We should add a CI test that does some basic grep'ing to verify that they're in sync.

Appendix: Other approaches

I also tried to keep a single source of truth - an MSRV.txt file in the repository root that was sourced by other files. I ran into a few problems:

• I was able to do the following to use that file to generate the crate-level doc comment:

  //! # Minimum Supported Rust Version (MSRV)
  //! 
  #![doc = concat!("zerocopy's MSRV is ", include_str!("../MSRV.txt"), ".")]

  ...unfortunately, the cargo readme tool we use to generate our README.md is not able to parse this, and so simply stops parsing the doc comment as soon as it encounters the #![doc = ...] line.
• In zerocopy-derive/tests/trybuild.rs, I wasn't able to replace #[rustversion::stable(1.61.0)] with an equivalent which used MSRV.txt