Use complete SHA to create and query commit status (#22244)

Fix #13485.

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/web/repo/commit.go

@@ -283,7 +283,7 @@ func Diff(ctx *context.Context) {
 		}
 		return
 	}
-	if len(commitID) != 40 {
+	if len(commitID) != git.SHAFullLength {
 		commitID = commit.ID.String()
 	}