Update ccpp.yml

Switch to ubuntu-20.04 and add a couple dev libs.

.github/workflows/ccpp.yml

@@ -9,12 +9,12 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
     - uses: actions/checkout@v2
     - name: prepare-packages
-      run: sudo apt-get install fakeroot acl libacl1-dev attr libattr1-dev liblz4-dev yodl
+      run: sudo apt-get install fakeroot acl libacl1-dev attr libattr1-dev liblz4-dev libzstd-dev libxxhash-dev yodl
     - name: prepare-source
       run: ./prepare-source
     - name: configure