Improve grammar in the import system reference documentation (GH-18209)

Replaced the period with a comma.

Automerge-Triggered-By: @Mariatta

Author: Bonifacio2

Doc/reference/import.rst

@@ -857,7 +857,7 @@ module.  ``find_spec()`` returns a fully populated spec for the module.
 This spec will always have "loader" set (with one exception).
 
 To indicate to the import machinery that the spec represents a namespace
-:term:`portion`. the path entry finder sets "loader" on the spec to
+:term:`portion`, the path entry finder sets "loader" on the spec to
 ``None`` and "submodule_search_locations" to a list containing the
 portion.