Add Valgrind installation verification step

This change adds a step to verify that Valgrind is installed correctly in the continuous integration workflow. Running `valgrind --version` ensures that the tool is available before proceeding further in the workflow, which helps in diagnosing any installation issues early.

.github/workflows/continuous-integration-pecl.yml

@@ -37,6 +37,9 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y autoconf automake libtool bison re2c valgrind
 
+      - name: Verify Valgrind installation
+        run: valgrind --version
+
       - name: Install Composer dependencies
         run: composer install --prefer-dist --no-progress