Extensions: don't include the extensions own temporary file

Exclude the extensions own temporary file when building an extension.
Even though this file should be removed, it's possible the build
process was killed for the system was turned off, so best explicitly
exclude the file.

bl_pkg/cli/blender_ext.py

@@ -1974,6 +1974,9 @@ class subcmd_author:
 
         filenames_root_exclude = {
             pkg_filename,
+            # It's possible a temporary file exists from a previous run which was not cleaned up.
+            # Although in general this should be cleaned up - power failure etc may mean it exists.
+            pkg_filename + "@",
             # This is added, converted from the TOML.
             PKG_REPO_LIST_FILENAME,