Test against PHP 8.0 and 8.1

Author: alcaeus

.travis.yml

@@ -101,7 +101,11 @@ jobs:
       env:
         - CONFIGURE_OPTS="--with-mongodb-client-side-encryption=no"
 
-    # Test with upcoming PHP version
+    # Test with PHP 8.0
+    - stage: Test
+      php: 8.0snapshot
+
+    # Test with PHP 8.1
     - stage: Test
       php: nightly