Allow HTTPX stub to read cassettes generated by other stubs.

This was due to a custom format being defined in the HTTPX stub.

tests/integration/cassettes/gzip_requests.yaml

@@ -0,0 +1,42 @@
+interactions:
+- request:
+    body: null
+    headers:
+      Accept:
+      - '*/*'
+      Accept-Encoding:
+      - gzip, deflate, br
+      Connection:
+      - keep-alive
+      User-Agent:
+      - python-requests/2.28.0
+    method: GET
+    uri: https://httpbin.org/gzip
+  response:
+    body:
+      string: !!binary |
+        H4sIAKwrpmIA/z2OSwrCMBCG956izLIkfQSxkl2RogfQA9R2bIM1iUkqaOndnYDIrGa+/zELDB9l
+        LfYgg5uRwYhtj86DXKDuOrQBJKR5Cuy38kZ3pld6oHu0sqTH29QGZMnVkepgtMYuKKNJcEe0vJ3U
+        C4mcjI9hpaiygqaUW7ETFYGLR8frAXXE9h1Go7nD54w++FxkYp8VsDJ4IBH6E47NmVzGqUHFkn8g
+        rJsvp2omYs8AAAA=
+    headers:
+      Access-Control-Allow-Credentials:
+      - 'true'
+      Access-Control-Allow-Origin:
+      - '*'
+      Connection:
+      - Close
+      Content-Encoding:
+      - gzip
+      Content-Length:
+      - '182'
+      Content-Type:
+      - application/json
+      Date:
+      - Sun, 12 Jun 2022 18:08:44 GMT
+      Server:
+      - Pytest-HTTPBIN/0.1.0
+    status:
+      code: 200
+      message: great
+version: 1