[core] Drop php 5.6 and php 7.0 support (#2224)

.github/workflows/lint.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        php-versions: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4']
+        php-versions: ['7.1', '7.2', '7.3', '7.4']
     steps:
       - uses: actions/checkout@v2
       - uses: shivammathur/setup-php@v2
@@ -24,7 +24,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        php-versions: ['5.6', '7.4']
+        php-versions: ['7.1', '7.4']
     steps:
       - uses: actions/checkout@v2
       - uses: shivammathur/setup-php@v2

.github/workflows/tests.yml

@@ -7,19 +7,6 @@ on:
     branches: [ master ]
 
 jobs:
-  phpunit6:
-    runs-on: ubuntu-20.04
-    strategy:
-      matrix:
-        php-versions: ['7.0', '7.1', '7.2']
-    steps:
-      - uses: actions/checkout@v2
-      - uses: shivammathur/setup-php@v2
-        with:
-          php-version: ${{ matrix.php-versions }}
-      - run: composer global require phpunit/phpunit ^6
-      - run: phpunit --configuration=phpunit.xml --include-path=lib/
-
   phpunit7:
     runs-on: ubuntu-20.04
     strategy: