openapi: Loosen anchor parameter specification to string.

Real requests would not validate against the previous version.  There
seems to be no consistent way to determine whether a string parameter
should be coerced to an integer for validation against an allOf
schema (which works at the level of JSON objects, not strings).

See also https://github.com/python-openapi/openapi-core/issues/698.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/openapi/openapi.py

@@ -486,7 +486,11 @@ def validate_request(
     # against the OpenAPI documentation.
     assert isinstance(data, dict)
     mock_request = MockRequest(
-        "http://localhost:9991/", method, "/api/v1" + url, headers=http_headers, args=data
+        "http://localhost:9991/",
+        method,
+        "/api/v1" + url,
+        headers=http_headers,
+        args={k: str(v) for k, v in data.items()},
     )
     try:
         openapi_spec.spec().validate_request(mock_request)

zerver/openapi/zulip.yaml

@@ -5994,7 +5994,7 @@ paths:
             2.1.x and older in the `found_newest` return value).
           schema:
             $ref: "#/components/schemas/Anchor"
-          example: 43
+          example: "43"
         - name: include_anchor
           in: query
           description: |
@@ -6863,7 +6863,7 @@ paths:
               query, if any; otherwise, the most recent message.
           schema:
             $ref: "#/components/schemas/Anchor"
-          example: 43
+          example: "43"
           required: true
         - name: include_anchor
           in: query
@@ -18147,13 +18147,7 @@ components:
         The event's type, relevant both for client-side dispatch and server-side
         filtering by event type in [POST /register](/api/register-queue).
     Anchor:
-      oneOf:
-        - type: string
-          enum:
-            - newest
-            - oldest
-            - first_unread
-        - type: integer
+      type: string
     Attachments:
       type: object
       description: |