FIX: Remove whitespace from theme git versions (#12857)

Followup to 0a6fab564f

lib/theme_store/git_importer.rb

@@ -51,7 +51,7 @@ class ThemeStore::GitImporter
   end
 
   def version
-    execute "git", "rev-parse", "HEAD"
+    execute("git", "rev-parse", "HEAD").strip
   end
 
   def cleanup!