fix: replace astral-sh/setup-uv action with shell install

The JS-based GitHub Action doesn't work on Gitea's act runner.
Use curl installer + GITHUB_PATH instead.

.gitea/workflows/ci.yml

@@ -18,10 +18,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Set up uv
-        uses: astral-sh/setup-uv@v7
-        with:
-          version: "latest"
-          activate-environment: false
+        run: curl -LsSf https://astral.sh/uv/install.sh | sh && echo "$HOME/.local/bin" >> $GITHUB_PATH
 
       - name: Set up Python
         run: uv python install 3.13
@@ -43,10 +40,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Set up uv
-        uses: astral-sh/setup-uv@v7
-        with:
-          version: "latest"
-          activate-environment: false
+        run: curl -LsSf https://astral.sh/uv/install.sh | sh && echo "$HOME/.local/bin" >> $GITHUB_PATH
 
       - name: Set up Python
         run: uv python install 3.13