*: end support for Go v1.20 (grpc#7250)

Author: dfawley

.github/workflows/testing.yml

@@ -64,8 +64,6 @@ jobs:
           - type: tests
             goversion: '1.21'
 
-          - type: tests
-            goversion: '1.20'
     steps:
       # Setup the environment.
       - name: Setup GOARCH

README.md

@@ -10,7 +10,7 @@ RPC framework that puts mobile and HTTP/2 first. For more information see the
 
 ## Prerequisites
 
-- **[Go][]**: any one of the **three latest major** [releases][go-releases].
+- **[Go][]**: any one of the **two latest major** [releases][go-releases].
 
 ## Installation