add mnemonic to modules_mapping

Author: tyler-french

gazelle/modules_mapping/def.bzl

@@ -43,6 +43,7 @@ def _modules_mapping_impl(ctx):
 
         ctx.actions.run(
             inputs = [whl],
+            mnemonic = "ModulesMapping",
             outputs = [wheel_modules_mapping],
             executable = ctx.executable._generator,
             arguments = [args],