message: ci: attempt to fix cross in CI
  This is a perfect example of why adding support for more targets is
  costly. Every so often, the cross compiling toolchain breaks for
  mysterious reasons.
diff: @@ -75,9 +75,11 @@ jobs:
  - name: Install and configure Cross
  if: matrix.target != ''
  run: |
  - # FIXME: to work around bugs in latest cross release, install master.
  - # See: https://github.com/rust-embedded/cross/issues/357
  - cargo install --git https://github.com/rust-embedded/cross
  + # We used to install 'cross' from master, but it kept failing. So now
  + # we build from a known-good version until 'cross' becomes more stable
  + # or we find an alternative. Notably, between v0.2.1 and current
  + # master (2022-06-14), the number of Cross's dependencies has doubled.
  + cargo install --bins --git https://github.com/rust-embedded/cross --tag v0.2.1
  echo "CARGO=cross" >> $GITHUB_ENV
  echo "TARGET=--target ${{ matrix.target }}" >> $GITHUB_ENV
  