.github: need valgrind for new memleak test

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

.github/workflows/build.yml

@@ -27,7 +27,7 @@ jobs:
       - name: Install dependencies
         run: |
           sudo apt-get -y update
-          sudo apt-get -y install tree tshark
+          sudo apt-get -y install tree tshark valgrind
       - uses: actions/checkout@v2
       - name: Configure
         run: |