Bump Go toolchain to 1.26.3

Agent-Logs-Url: https://github.com/cli/cli/sessions/74d21df5-9f54-4a76-97ee-7b2e2d7bd6be

Co-authored-by: BagToad <47394200+BagToad@users.noreply.github.com>

Author: Copilot

go.mod

@@ -2,7 +2,7 @@ module github.com/cli/cli/v2
 
 go 1.26.0
 
-toolchain go1.26.2
+toolchain go1.26.3
 
 require (
 	charm.land/bubbles/v2 v2.1.0