CI: Updated nightly version and locked cargo-expand install

The updated nightly version fixes a bug with the
'match_block_trailing_comma' rustfmt config.
Previously not all missing commas were caught.
Probably related to rust-lang/rustfmt#4998.

When installing cargo-expand, we now use '--locked' to ensure
lock-files are used.
This is a workaround for the release of v4.7.0 of the 'syntect' crates,
which violated semantic versioning. Using the lock files avoids this
version. For details see sharkdp/bat#1991.

Author: Emoun

.github/actions/run-test-groups/action.yml

@@ -25,7 +25,7 @@ runs:
         # Install dependencies of 'macrotest'
         rustup toolchain install nightly
         # Can only use stable rust to build cargo-expand because it doesn't build on 1.34
-        cargo +stable install cargo-expand
+        cargo +stable install --locked cargo-expand
         # Set the rust version to use for this build
         rustup default ${{ inputs.rust-version }}
     - run: echo "::group::Test no_features"

.github/workflows/rust.yml

@@ -48,7 +48,7 @@ jobs:
     name: Rustfmt
     runs-on: ubuntu-latest
     env:
-      RUSTV: nightly-2021-06-08    
+      RUSTV: nightly-2021-12-26
     steps:
       - uses: actions/checkout@v2
       - name: Install