all: add/bump tested Go versions

Add 1.18.1.

Bump 1.16.0 -> 1.16.15, 1.17.3 -> 1.17.10.

Change-Id: Ic19b47004484970b404e4eb8b2d02955410f65af
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/406839
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Lasse Folger <lassefolger@google.com>
diff --git a/integration_test.go b/integration_test.go
index 8a4f7af..f0d5e5e 100644
--- a/integration_test.go
+++ b/integration_test.go
@@ -38,7 +38,7 @@
 	protobufVersion = "3.15.3"
 	protobufSHA256  = "" // ignored if protobufVersion is a git hash
 
-	golangVersions = []string{"1.11.13", "1.12.17", "1.13.15", "1.14.15", "1.15.15", "1.16.10", "1.17.3"}
+	golangVersions = []string{"1.11.13", "1.12.17", "1.13.15", "1.14.15", "1.15.15", "1.16.15", "1.17.10", "1.18.1"}
 	golangLatest   = golangVersions[len(golangVersions)-1]
 
 	staticcheckVersion = "2020.1.4"