all: release v1.28.0

Change-Id: Ied1d78a3cc0d417fbbd1d10d30730173af3e20d4
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/391414
Reviewed-by: Joseph Tsai <[email protected]>
Reviewed-by: Damien Neil <[email protected]>

Author: lfolger

internal/version/version.go

@@ -52,9 +52,9 @@ import (
 //	10. Send out the CL for review and submit it.
 const (
 	Major      = 1
-	Minor      = 27
-	Patch      = 1
-	PreRelease = "devel"
+	Minor      = 28
+	Patch      = 0
+	PreRelease = ""
 )
 
 // String formats the version string for this module in semver format.