Changes build to test go 1.21rc2 (#1571)

Signed-off-by: Adrian Cole <adrian@tetrate.io>

internal/platform/platform.go

@@ -5,12 +5,17 @@
 package platform
 
 import (
+	"regexp"
 	"runtime"
-	"strings"
 )
 
-// TODO: IsAtLeastGo120
-var IsGo120 = strings.Contains(runtime.Version(), "go1.20")
+// IsAtLeastGo120 checks features added in 1.20. We can remove this when Go
+// 1.22 is out.
+var IsAtLeastGo120 = isAtLeastGo120(runtime.Version())
+
+func isAtLeastGo120(version string) bool {
+	return regexp.MustCompile("go1.[2-9][0-9][^0-9]").MatchString(version)
+}
 
 // archRequirementsVerified is set by platform-specific init to true if the platform is supported
 var archRequirementsVerified bool