CI: fix the document action for divergent branches.

This was never intended to merge anything.

.github/workflows/main.yaml

@@ -60,9 +60,9 @@ jobs:
         uses: actions/checkout@v3
         with:
           fetch-depth: 0
-      - name: Pull tags from upstream repository
+      - name: Fetch tags from upstream repository
         run: |
-          git pull --tags https://github.com/amaranth-lang/amaranth.git
+          git fetch --tags https://github.com/amaranth-lang/amaranth.git
       - name: Set up Python
         uses: actions/setup-python@v4
         with: