ci: Add graphviz to macOS install

(Attempt to) fix missing gvpack error when running docs tests.

Author: KrystalDelusion

.github/actions/setup-build-env/action.yml

@@ -14,7 +14,7 @@ runs:
       if: runner.os == 'macOS'
       shell: bash
       run: |
-        HOMEBREW_NO_INSTALLED_DEPENDENTS_CHECK=1 brew install bison flex gawk libffi pkg-config bash
+        HOMEBREW_NO_INSTALLED_DEPENDENTS_CHECK=1 brew install bison flex gawk libffi pkg-config bash graphviz
 
     - name: Linux runtime environment
       if: runner.os == 'Linux'