CI: Linux tests in the Gitea job's image, since the hosted image's zsh and fish break the shell tests

.github/workflows/ci.yml

@@ -28,15 +28,25 @@ jobs:
 
   linux:
     runs-on: ubuntu-24.04
+    # A clean image: the hosted one's zsh and fish setup breaks the shell tests.
+    container: docker.gitea.com/runner-images:ubuntu-24.04
     env:
       CARGO_PROFILE_DEV_DEBUG: 0
     steps:
       - uses: actions/checkout@v7
+      # The job container comes without rustup.
+      - run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --no-modify-path --default-toolchain none
+          echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
       - run: rustup toolchain install --no-self-update
       - uses: Swatinem/rust-cache@v2
+      # The job container runs as root, which ignores the file permissions the tests check.
       - run: |
-          sudo apt-get update && sudo apt-get install -y --no-install-recommends pkg-config libwayland-dev \
+          apt-get update && apt-get install -y --no-install-recommends pkg-config libwayland-dev \
             libxkbcommon-dev libxkbcommon-x11-dev libxcb1-dev libx11-xcb-dev libfontconfig-dev \
             libfreetype-dev zsh fish xvfb
-      - run: cargo test --locked --quiet
+          useradd --create-home ci
+          chmod o+x "$HOME"
+          chown -R ci "$GITHUB_WORKSPACE" "$HOME/.cargo" "$HOME/.rustup"
+          runuser -u ci -- env HOME=/home/ci CARGO_HOME="$HOME/.cargo" RUSTUP_HOME="$HOME/.rustup" PATH="$PATH" cargo test --locked --quiet
       - run: cargo build --locked