Update integration tests to use WordPress 5.9

.github/workflows/integrate.yml

@@ -13,22 +13,18 @@ jobs:
 
     strategy:
       matrix:
-        wordpress: [ '5.7', '6.3' ]
-        php: [ '7.4', '8.0', '8.2' ]
+        wordpress: [ '5.9', '6.5' ]
+        php: [ '7.4', 'latest' ]
         allowed_failure: [ false ]
         include:
           # Check upcoming WP.
-          - php: '8.2'
+          - php: 'latest'
             wordpress: 'trunk'
             allowed_failure: true
           # Check upcoming PHP.
-          - php: '8.3'
+          - php: '8.4'
             wordpress: 'latest'
             allowed_failure: true
-        exclude:
-          # WordPress 5.7 doesn't support PHP 8.2.
-          - php: '8.2'
-            wordpress: '5.7'
       fail-fast: false
 
     steps:
@@ -43,11 +39,6 @@ jobs:
           ini-values: ${{ matrix.ini-values }}
           coverage: ${{ matrix.coverage }}
 
-      - name: Install PHPUnit 7.x for WP < 5.9
-        if: ${{ matrix.wordpress < 5.9 }}
-        # Ignore platform requirements, so that PHPUnit 7.5 can be installed on PHP 8.0 (and above).
-        run: composer require --dev phpunit/phpunit:"^7.5" --ignore-platform-req=php+ --no-update --no-scripts --no-interaction
-
       - name: Install Composer dependencies
         uses: ramsey/composer-install@v2
         with: