Rewrite of GitHub Actions

.github/actions/setup-misc/action.yml

@@ -0,0 +1,55 @@
+name: 'Set up misc test dependencies'
+description: >-
+  Installs the apt and pip dependencies required by the `misc` test script,
+  with caching of both apt packages and the pip download cache so subsequent
+  runs avoid re-downloading and re-unpacking the (large) texlive packages.
+
+runs:
+  using: composite
+  steps:
+    - name: Cache and install apt packages
+      uses: awalsh128/cache-apt-pkgs-action@v1
+      with:
+        # Bump `version` to invalidate the cache after meaningful changes.
+        version: 1
+        packages: >-
+          asciidoctor
+          autoconf
+          devscripts
+          dia
+          hevea
+          latexmk
+          libasound2-dev
+          libcups2-dev
+          libfontconfig1-dev
+          librsvg2-bin
+          libx11-dev
+          libxext-dev
+          libxrandr-dev
+          libxrender-dev
+          libxt-dev
+          libxtst-dev
+          pdf2svg
+          python3-pip
+          rsync
+          shellcheck
+          shfmt
+          texlive-font-utils
+          texlive-fonts-recommended
+          texlive-latex-base
+          texlive-latex-extra
+          texlive-latex-recommended
+
+    - name: Cache pip download cache
+      uses: actions/cache@v4
+      with:
+        path: ~/.cache/pip
+        key: ${{ runner.os }}-pip-misc-v1
+        restore-keys: |
+          ${{ runner.os }}-pip-misc-
+
+    - name: Install Python tools
+      shell: bash
+      # PEP 668: Ubuntu 24.04's system Python is externally-managed.
+      # `--break-system-packages` is the documented escape hatch for CI.
+      run: pip install --break-system-packages black flake8 html5validator