tests: constrain http pytest to tests/http directory

Running the http pytest had to be done from tests directory or above,
because the repeat argument fixture was defined in tests/conftest.py.
However, the repeat argument is not needed because its functionality
can be provided by pytest-repeat as documented in the test's
README.md. So, removed the pytest_addoption function for the repeat
argument and the pytest_report_header function is moved to
tests/http/conftest.py.

TODO: Remove repeat argument from all tests. As a stopgap, a
one-element list is defined for it for now.

Closes #14611

.github/workflows/http3-linux.yml

@@ -470,7 +470,7 @@ jobs:
         env:
           TFLAGS: "${{ matrix.build.tflags }}"
 
-      - run: pytest -v tests
+      - run: pytest -v tests/http
         name: 'run pytest'
         env:
           TFLAGS: "${{ matrix.build.tflags }}"

.github/workflows/linux.yml

@@ -487,10 +487,10 @@ jobs:
           make V=1 VERBOSE=1 test-ci
 
       - if: contains(matrix.build.install_steps, 'pytest')
-        # run for `tests` directory, so pytest does not pick up any other
+        # run for `tests/http` directory, so pytest does not pick up any other
         # packages we might have built here
         run:
-          pytest -v tests
+          pytest -v tests/http
         name: 'run pytest'
         env:
           TFLAGS: "${{ matrix.build.tflags }}"