Update PHP and PHPUnit across all packages; fix ext-rdkafka requirement

Author: andrewmy

composer.json

@@ -10,13 +10,13 @@
   "homepage": "https://enqueue.forma-pro.com/",
   "license": "MIT",
   "require": {
-    "php": "^7.1.3",
+    "php": "^7.3",
     "queue-interop/queue-interop": "^0.8",
     "mongodb/mongodb": "^1.2",
     "ext-mongodb": "^1.5"
   },
   "require-dev": {
-    "phpunit/phpunit": "~7.5",
+    "phpunit/phpunit": "^9.5",
     "queue-interop/queue-spec": "^0.6",
     "enqueue/test": "0.10.x-dev",
     "enqueue/null": "0.10.x-dev"