Removes arrow higher limits for plexus provider (apache#16026)

Plexus provider needlessly limits arrow to <1.0.0. This was added
in apache#14781 to fix failing tests, but Plexus uses arrow in a very
limited way and it turned out that just checking for None value
before running arrow.get(), fixes the problem (and we can upgrade
to latest version of arrow as well).

(cherry picked from commit 5dd0802)

airflow/providers/plexus/hooks/plexus.py

@@ -67,7 +67,7 @@ def _generate_token(self) -> Any:
     def token(self) -> Any:
         """Returns users token"""
         if self.__token is not None:
-            if arrow.get(self.__token_exp) <= arrow.now():
+            if not self.__token_exp or arrow.get(self.__token_exp) <= arrow.now():
                 self.__token = self._generate_token()
             return self.__token
         else:

setup.py

@@ -416,7 +416,7 @@ def get_sphinx_theme_version() -> str:
     'pinotdb>0.1.2,<1.0.0',
 ]
 plexus = [
-    'arrow>=0.16.0,<1.0.0',
+    'arrow>=0.16.0',
 ]
 postgres = [
     'psycopg2-binary>=2.7.4',