build: add valgrind ci workflow for memory issue detection

This commit introduces a GitHub Actions workflow (`valgrind.yml`)
to detect memory issues in the `argtable3` project using Valgrind.
The workflow runs on `push` and `pull_request` events targeting
the `master` branch, as well as manually via `workflow_dispatch`.

Purpose:
- Use Valgrind to identify memory leaks and invalid memory accesses.
- Automate memory issue detection during CI to improve code quality.

Author: tomghuang

.github/workflows/valgrind.yml

@@ -0,0 +1,33 @@
+name: Valgrind
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [ master ]
+  pull_request:
+
+jobs:
+  valgrind-check:
+    name: Valgrind Memory Check
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout Code
+      uses: actions/checkout@v3
+
+    - name: Install Dependencies
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y build-essential cmake valgrind
+
+    - name: Build Project
+      run: |
+        mkdir -p build
+        cd build
+        cmake -DCMAKE_BUILD_TYPE=Debug ..
+        make
+
+    - name: Run Tests with Valgrind
+      run: |
+        cd build
+        valgrind --leak-check=full --show-leak-kinds=all --error-exitcode=1 tests/test_src