pytest: improvements

- set CURL_CI for pytest runs in CI environments
- exclude timing sensitive tests from CI runs
- for failed results, list only the log and stat of
  the failed transfer

- fix type in http.c comment

Closes #11812

.github/workflows/linux.yml

@@ -404,7 +404,8 @@ jobs:
       # run for `tests` directory, so pytest does not pick up any other
       # packages we might have built here
       run:
-        pytest -v tests
+        pytest tests
       name: 'run pytest'
       env:
         TFLAGS: "${{ matrix.build.tflags }}"
+        CURL_CI: github