Switch typing '|' to Union

Py3.9 and before doesn't understand the "type | type" form.

charmhub_lp_tools/charm_project.py

@@ -19,7 +19,8 @@
 import logging
 import subprocess
 import tempfile
-from typing import (Any, Dict, Generator, List, Tuple, IO, Optional, Set)
+from typing import (Any, Dict, Generator, List, Tuple, IO, Optional, Set,
+                    Union)
 import sys
 import time
 import yaml
@@ -1863,7 +1864,7 @@ def copy_revisions(self,
                 CharmChannel.str_revisions_by_arch(destination_arch_revisions))
 
             # don't duplicate releases to the same channel.
-            revision_pairs: Set[Tuple[int, int | None]] = set()
+            revision_pairs: Set[Tuple[int, Union[int, None]]] = set()
             for arch, revision in arch_revisions.items():
                 dest_revision = destination_arch_revisions.get(arch)
                 if (revision, dest_revision) in revision_pairs:

charmhub_lp_tools/revisions.py

@@ -24,6 +24,7 @@
     Dict,
     List,
     Set,
+    Union,
 )
 
 from prettytable import PrettyTable
@@ -94,8 +95,8 @@ def setup_parser(
 
 
 def get_revisions(channel: CharmChannel,
-                  args_bases: List[str] | None,
-                  args_arches: List[str] | None
+                  args_bases: Union[List[str], None],
+                  args_arches: Union[List[str], None],
                   ) -> Dict[str, Dict[str, List[int]]]:
     """Get the revisions by base -> arch -> [revisions].