fix tests on py3.6 and lint on 3.9 (#108)

* fix tests on py3.6

* fix pre-commit rst backticks

Author: graingert

README.rst

@@ -218,9 +218,9 @@ may need to be setup or torn down for the test (the exact affected
 fixtures depends on which scope they are and whether other tests will
 still use the same fixture).  If the timeouts really are too short to
 include fixture durations, firstly make the timeouts larger ;).  If
-this really isn't an option a `timeout_func_only` boolean setting
+this really isn't an option a ``timeout_func_only`` boolean setting
 exists which can be set in the pytest ini configuration file, as
-documented in `pytest --help`.
+documented in ``pytest --help``.
 
 
 Debugger Detection

test_pytest_timeout.py

@@ -87,7 +87,7 @@ def test_foo():
     """
     )
     result = testdir.runpytest(
-        "--timeout=1", "--cov=test_cov.py", "--timeout-method=thread"
+        "--timeout=1", "--cov=test_cov", "--timeout-method=thread"
     )
     result.stderr.fnmatch_lines(
         [