Remove DB matrix again as it does not work

Author: schlessera

.github/workflows/testing.yml

@@ -58,44 +58,28 @@ jobs:
         run: composer phpunit
 
   functional: #----------------------------------------------------------------------
-    name: Functional - WP ${{ matrix.wp }} on PHP ${{ matrix.php }} (${{ matrix.db }})
+    name: Functional - WP ${{ matrix.wp }} on PHP ${{ matrix.php }}
     strategy:
       fail-fast: false
       matrix:
         php: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4']
         wp: ['latest']
-        db: ['mysql:5.7']
         test: ["composer behat || composer behat-rerun"]
         include:
           - php: '5.6'
             wp: 'trunk'
-            db: 'mysql:5.7'
             test: "composer behat || composer behat-rerun"
           - php: '7.4'
             wp: 'trunk'
-            db: 'mysql:5.7'
-            test: "composer behat || composer behat-rerun"
-          - php: '7.4'
-            wp: 'latest'
-            db: 'mysql:8.0'
-            test: "composer behat || composer behat-rerun"
-          - php: '7.4'
-            wp: 'latest'
-            db: 'mysql:5.6'
-            test: "composer behat || composer behat-rerun"
-          - php: '7.4'
-            wp: 'latest'
-            db: 'mariadb:10.1'
             test: "composer behat || composer behat-rerun"
           - php: '5.6'
             wp: '3.7'
-            db: 'mysql:5.7'
             test: "composer behat || composer behat-rerun || true"
     runs-on: ubuntu-latest
 
     services:
       mysql:
-        image: ${{ matrix.db }}
+        image: mysql:5.7
         env:
           MYSQL_DATABASE: wp_cli_test
           MYSQL_USER: root