Validate version against Cargo.toml

This is strongly inspired by an analogous check in the ripgrep
workflow, but done differently (from how that currently does it) by
parsing `Cargo.toml` using `yq`.

The `yq` command supports reading TOML (just not writing it). This
command is present on the `ubuntu-latest` runner.

This also moves the "Show the version" step into the new step, and
has that step also show the version extracted from `Cargo.toml`, so
as to make errors easier to understand and also to help verify that
this logic is really working.

.github/workflows/release.yml

@@ -30,16 +30,31 @@ jobs:
 #      VERSION: TEST-0.0.0
 
     steps:
-      - name: Create artifacts directory
-        run: mkdir artifacts
+      - name: Checkout repository
+        uses: actions/checkout@v4
 
       - name: Get the release version from the tag
         if: env.VERSION == ''
         run: echo 'VERSION=${{ github.ref_name }}' >> "$GITHUB_ENV"
 
-      - name: Show the version
+      - name: Validate version against Cargo.toml
         run: |
-          echo "version is: $VERSION"
+          manifest_version="$(yq -r .package.version Cargo.toml)"
+          echo "version to give the release: $VERSION"
+          echo "version Cargo.toml declares: $manifest_version"
+
+          case "$VERSION" in
+          "$manifest_version")
+            echo "OK: Version to give the relase agrees with top-level Cargo.toml."
+            ;;
+          *)
+            echo "STOPPING: Version to give the release seems mistaken."
+            exit 1
+            ;;
+          esac
+
+      - name: Create artifacts directory
+        run: mkdir artifacts
 
       - name: Create GitHub release
         id: release