requirements: upgrade pytest to 4.6.3

This allows us to use pytest-subtests [1], which makes it easier to
write tests with assertions for multiple related values without
rewriting them to use dicts or sets.

[1] https://github.com/pytest-dev/pytest-subtests

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>

requirements.txt

@@ -2,7 +2,7 @@ attrs==19.1.0
 jinja2==2.10.1
 pexpect==4.7
 https://github.com/labgrid-project/pyserial/archive/v3.4.0.1.zip#egg=pyserial
-pytest==4.0.2
+pytest==4.6.3
 pyudev==0.21.0
 requests==2.22.0
 xmodem==0.4.5