Bump py from 1.8.0 to 1.8.1 in /requirements (#5910)

Bumps [py](https://github.com/pytest-dev/py) from 1.8.0 to 1.8.1.
- [Release notes](https://github.com/pytest-dev/py/releases)
- [Changelog](https://github.com/pytest-dev/py/blob/master/CHANGELOG)
- [Commits](https://github.com/pytest-dev/py/compare/1.8.0...1.8.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements/dev.txt

@@ -65,9 +65,9 @@ packaging==19.1 \
 pluggy==0.13.0 \
     --hash=sha256:0db4b7601aae1d35b4a033282da476845aa19185c1e6964b25cf324b5e4ec3e6 \
     --hash=sha256:fa5fa1622fa6dd5c030e9cad086fa19ef6a0cf6d7a2d12318e10cb49d6d68f34
-py==1.8.0 \
-    --hash=sha256:64f65755aee5b381cea27766a3a147c3f15b9b6b9ac88676de66ba2ae36793fa \
-    --hash=sha256:dc639b046a6e2cff5bbe40194ad65936d6ba360b52b3c3fe1d08a82dd50b5e53
+py==1.8.1 \
+    --hash=sha256:c20fdd83a5dbc0af9efd622bee9a5564e278f6380fffcacc43ba6f43db2813b0 \
+    --hash=sha256:5e27081401262157467ad6e7f851b7aa402c5852dbcb3dae06768434de5752aa
 pyparsing==2.4.2 \
     --hash=sha256:d9338df12903bbf5d65a0e4e87c2161968b10d2e489652bb47001d82a9b028b4
 wcwidth==0.1.8 \