build/github_repository: fix wrong template arg

Change-Id: Id29f781e05cc8902ae37874eebf358352a9d6f76
Reviewed-on: https://review.monogon.dev/c/monogon/+/3966
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/build/github_repository/def.bzl b/build/github_repository/def.bzl
index bcb205f..81a7268 100644
--- a/build/github_repository/def.bzl
+++ b/build/github_repository/def.bzl
@@ -81,7 +81,7 @@
         )
         if integrity == "":
             # buildifier: disable=print
-            print("Missing integrity for submodule \"{submodule}\": \"{sha256}\". Consider adding it.".format(
+            print("Missing integrity for submodule \"{submodule}\": \"{integrity}\". Consider adding it.".format(
                 submodule = submodule,
                 integrity = download_info.integrity,
             ))