general: cmake: add ZINT_SANITIZEM (clang -fsanitize=memory) option

and suppress errors in lib and backend tests (pretty sure they're
  nearly all false positives apart from maybe 2 non-initializations
  in "gif.c" (`pOut` buffer) and "raster.c" (`rotated_pixbuf`)
github: install de_DE.UTF-8 locale in ubuntu-debug also

.github/workflows/ci.yml

@@ -65,6 +65,10 @@ jobs:
     - name: Install libpng-dev
       run: sudo apt-get install libpng-dev
 
+    - name: Install locale
+      shell: bash
+      run: sudo locale-gen de_DE.UTF-8 && sudo update-locale
+
     - name: Create Build Environment
       run: cmake -E make_directory ${{runner.workspace}}/build