Update tested driver versions

Author: alcaeus

.evergreen/config.yml

@@ -439,7 +439,7 @@ axes:
         variables:
           DRIVER_VERSION: "1.8.1"
       - id: "latest-stable"
-        display_name: "1.8-stable"
+        display_name: "1.9-stable"
         variables:
           DRIVER_VERSION: "stable"
       - id: "1.8-dev"

.travis.yml

@@ -51,17 +51,13 @@ jobs:
     # Test against PHP 8
     - stage: Test
       php: "8.0snapshot"
-      env:
-        - DRIVER_VERSION="1.9.0RC1"
     - stage: Test
       php: "8.0snapshot"
       env:
-        - DRIVER_VERSION="1.9.0RC1"
         - DEPLOYMENT=REPLICASET
     - stage: Test
       php: "8.0snapshot"
       env:
-        - DRIVER_VERSION="1.9.0RC1"
         - DEPLOYMENT=SHARDED_CLUSTER_RS
 
 before_install: