make HTTP caching headers optional

Author: ytausch

conda_forge_tick/git_utils.py

@@ -939,7 +939,7 @@ def create_pull_request(
 
         # fields like ETag and Last-Modified are stored in the response headers, we need to extract them
         header_fields = {
-            k: self._github3_session.last_response_headers[k]
+            k: self._github3_session.last_response_headers.get(k, None)
             for k in PullRequestDataValid.HEADER_FIELDS
         }
 

conda_forge_tick/models/pr_json.py

@@ -100,6 +100,8 @@ class PullRequestDataValid(ValidatedBaseModel):
     }
     """
     A set of all header fields that are stored in the PR object.
+    Header fields are assumed to be used for caching purposes and always optional.
+    The corresponding fields should be set to None if they are not present in the response.
     """
 
     e_tag: str | None = Field(None, alias="ETag")