Update CI workflow to exclude PHP 7.3

Removed PHP 7.3 from the CI workflow matrix.

Author: donatj

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         operating-system: [ ubuntu-latest ]
-        php-versions: [ '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4' ]
+        php-versions: [ '7.4', '8.0', '8.1', '8.2', '8.3', '8.4' ]
         psr-http-versions: [ '~1.0.0', '^1', '^2' ]
         exclude:
           - php-versions: '7.3'