CI: Make webpack cache key dynamic by Node major and drop build.mjs hash

- Export Node major to GITHUB_ENV for use in cache key
- Avoid hardcoding node20 in cache key; use node${env.NODE_MAJOR}
- Remove build.mjs from cache key; rely on webpack buildDependencies invalidation

This keeps cache keys portable across Node upgrades while avoiding
unnecessary cache misses. Webpack will invalidate restored caches when
build.mjs changes via buildDependencies.

Author: PeterDaveHello

.github/workflows/pre-release-build.yml

@@ -24,6 +24,8 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 20
+      - name: Detect Node major version
+        run: echo "NODE_MAJOR=$(node -p 'process.versions.node.split(".")[0]')" >> $GITHUB_ENV
       - name: Cache npm cache
         uses: actions/cache@v4
         with:
@@ -38,9 +40,9 @@ jobs:
           path: |
             .cache/webpack
             node_modules/.cache/webpack
-          key: ${{ runner.os }}-node20-webpack-${{ hashFiles('build.mjs') }}-${{ hashFiles('**/package-lock.json') }}
+          key: ${{ runner.os }}-node${{ env.NODE_MAJOR }}-webpack-${{ hashFiles('**/package-lock.json') }}
           restore-keys: |
-            ${{ runner.os }}-node20-webpack-
+            ${{ runner.os }}-node${{ env.NODE_MAJOR }}-webpack-
       - run: npm run build
 
       - uses: josStorer/get-current-time@v2