Add valgrind to C tests

Author: jeromekelleher

.github/workflows/ci.yml

@@ -88,3 +88,7 @@ jobs:
         run: |
           ninja -C build coverage-text
           cat build/meson-logs/coverage.txt
+      - name: Valgrind 
+        working-directory: ./lib
+        run: |
+          valgrind --leak-check=full --error-exitcode=1 ./build/tests