run clippy on the MSRV

.github/workflows/checks.yml

@@ -27,6 +27,13 @@ jobs:
           path: target
           key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
 
+      - uses: actions-rs/toolchain@v1
+        with:
+          # Fixed version for clippy lints.  Bump this as necesary.  It must not
+          # be older than the MSRV in tests.yml.
+          toolchain: "1.54"
+          override: true
+
       - uses: actions-rs/cargo@v1.0.1
         with:
           command: check

.github/workflows/tests.yml

@@ -12,7 +12,8 @@ jobs:
     strategy:
       matrix:
         rust:
-          - "1.47" # MSRV
+          # MSRV; most not be higher than the clippy rust version in checks.yml
+          - "1.47"
           - "stable"
         os:
           - ubuntu-latest