Install/run pre-commit directly

The update to Python 3.12 has broken the pre-commit action (as it
installs via pip rather than pipx). The maintainer seems unwilling to
fix it (to put it diplomatically), so let's just stop using the action
and imlement it ourselves.

.github/workflows/main-ci.yml

@@ -30,8 +30,16 @@ jobs:
     - name: ⚒️ Build
       run: ./gradlew assemble || ./gradlew assemble
 
+    - name: Cache pre-commit
+      uses: actions/cache@v4
+      with:
+        path: ~/.cache/pre-commit
+        key: pre-commit-3|${{ env.pythonLocation }}|${{ hashFiles('.pre-commit-config.yaml') }}
+
     - name: 💡 Lint
-      uses: pre-commit/action@v3.0.0
+      run: |
+        pipx install pre-commit
+        pre-commit run --show-diff-on-failure --color=always
 
     - name: 🧪 Run tests
       run: ./gradlew test validateMixinNames checkChangelog