CI: test against RabbitMQ 4.2.x, too

Author: michaelklishin

.github/workflows/ci.yaml

@@ -45,6 +45,7 @@ jobs:
         rabbitmq-series:
           - "4.0"
           - "4.1"
+          - "4.2"
         rust-version:
           - stable
           - beta
@@ -85,6 +86,7 @@ jobs:
       matrix:
         rabbitmq-series:
           - "4.1"
+          - "4.2"
         rust-version:
           - stable
         runner: