Bump version to 1.26.0-pre1

BUILD

@@ -81,7 +81,7 @@ g_stands_for = "gon"
 
 core_version = "9.0.0"
 
-version = "1.26.0-dev"
+version = "1.26.0-pre1"
 
 GPR_PUBLIC_HDRS = [
     "include/grpc/support/alloc.h",

build.yaml

@@ -15,7 +15,7 @@ settings:
   core_version: 9.0.0
   csharp_major_version: 2
   g_stands_for: gon
-  version: 1.26.0-dev
+  version: 1.26.0-pre1
 filegroups:
 - name: alts_tsi
   headers:

doc/g_stands_for.md

@@ -25,4 +25,4 @@
 - 1.23 'g' stands for ['gangnam'](https://github.com/grpc/grpc/tree/v1.23.x)
 - 1.24 'g' stands for ['ganges'](https://github.com/grpc/grpc/tree/v1.24.x)
 - 1.25 'g' stands for ['game'](https://github.com/grpc/grpc/tree/v1.25.x)
-- 1.26 'g' stands for ['gon'](https://github.com/grpc/grpc/tree/master)
+- 1.26 'g' stands for ['gon'](https://github.com/grpc/grpc/tree/v1.26.x)