[tests] use PHP 7.4 (#35)

Author: danepowell

.github/workflows/orca.yml

@@ -38,13 +38,13 @@ jobs:
           - ISOLATED_TEST_ON_NEXT_MINOR_DEV
           - INTEGRATED_UPGRADE_TEST_TO_NEXT_MINOR_DEV
           - LOOSE_DEPRECATED_CODE_SCAN
-        php-version: [ "7.3" ]
+        php-version: [ "7.4" ]
         include:
           - orca-job: ISOLATED_TEST_ON_CURRENT
             php-version: "8.0"
 
           # Custom job
-          - php-version: "7.3"
+          - php-version: "7.4"
             orca-job: ""
 
     steps: