all: start v1.26.0-devel

Change-Id: I544bd53c41794d5da2d381d3b182293a465f3c4b
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/302753
Trust: Joe Tsai <joetsai@digital-static.net>
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/version/version.go b/internal/version/version.go
index 5879131..ae0f5c0 100644
--- a/internal/version/version.go
+++ b/internal/version/version.go
@@ -54,7 +54,7 @@
 	Major      = 1
 	Minor      = 26
 	Patch      = 0
-	PreRelease = ""
+	PreRelease = "devel"
 )
 
 // String formats the version string for this module in semver format.