Adjust token expiry window to 40 seconds because of Azure (#392)

## Changes

Align with databricks/databricks-sdk-go#617 and
databricks/databricks-sdk-js#63

## Tests
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- [x] `make test` run locally
- [x] `make fmt` applied
- [ ] relevant integration tests applied

Signed-off-by: Serge Smertin <[email protected]>

databricks/sdk/oauth.py

@@ -57,7 +57,9 @@ class Token:
     def expired(self):
         if not self.expiry:
             return False
-        potentially_expired = self.expiry - timedelta(seconds=10)
+        # Azure Databricks rejects tokens that expire in 30 seconds or less,
+        # so we refresh the token 40 seconds before it expires.
+        potentially_expired = self.expiry - timedelta(seconds=40)
         now = datetime.now(tz=potentially_expired.tzinfo)
         is_expired = potentially_expired < now
         return is_expired