CI: Set up go

Needed for the vacuum pre-commit hook.

Signed-off-by: Stephen Finucane <stephen@that.guru>

.github/workflows/ci.yaml

@@ -14,6 +14,10 @@ jobs:
         uses: actions/setup-python@v4
         with:
           python-version: "3.12"
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: "1.21"
       - name: Install dependencies
         run: python -m pip install tox
       - name: Run tox