Lock Ubuntu version

Author: schlessera

.github/workflows/code-quality.yml

@@ -6,7 +6,11 @@ jobs:
 
   lint: #-----------------------------------------------------------------------
     name: Lint PHP files
-    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        php: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0']
+    runs-on: ubuntu-20.04
     steps:
       - name: Check out source code
         uses: actions/checkout@v2
@@ -55,7 +59,7 @@ jobs:
 
   phpcs: #----------------------------------------------------------------------
     name: PHPCS
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
       - name: Check out source code

.github/workflows/testing.yml

@@ -10,7 +10,7 @@ jobs:
       fail-fast: false
       matrix:
         php: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0']
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
       - name: Check out source code
@@ -99,7 +99,7 @@ jobs:
             wp: '3.7'
             mysql: '5.6'
             test: "composer behat || composer behat-rerun"
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     services:
       mysql: