Update requirements.txt

Author: BethanyG

requirements.txt

@@ -1,4 +1,4 @@
 # cmccandless: Breaking changes in pytest 5.4.0
 # Changelog: https://docs.pytest.org/en/stable/changelog.html#pytest-5-4-0-2020-03-12
 pytest ~= 6.2.5
-pytest-subtests>=0.4.0
+pytest-subtests~=0.5.0