Merge branch 'bump-PyYAML' into 'master'

Bump Python requirement PyYAML to 5.3.1

See merge request !984

requirements.txt

@@ -20,7 +20,7 @@ idna==2.10
 python-gitlab==1.7.0
 python-memcached==1.59
 pytz>=2018.7
-PyYAML==5.1
+PyYAML==5.3.1
 requests==2.24.0
 responses==0.10.7
 sentry-sdk==0.18.0