Upgrade pyaml from 5.3.1 to 5.4.1 (#11486)

5.4.1 (2021-01-20)

* yaml/pyyaml#480 -- Fix stub compat with older pyyaml versions that may unwittingly load it

5.4 (2021-01-19)

* yaml/pyyaml#407 -- Build modernization, remove distutils, fix metadata, build wheels, CI to GHA
* yaml/pyyaml#472 -- Fix for CVE-2020-14343, moves arbitrary python tags to UnsafeLoader
* yaml/pyyaml#441 -- Fix memory leak in implicit resolver setup
* yaml/pyyaml#392 -- Fix py2 copy support for timezone objects
* yaml/pyyaml#378 -- Fix compatibility with Jython

https://github.com/yaml/pyyaml/blob/master/CHANGES

3rdparty/python/constraints.txt

@@ -1,4 +1,4 @@
-# Generated by build-support/bin/generate_lockfile.sh on Thu Jan  7 05:28:27 PM PST 2021
+# Generated by build-support/bin/generate_lockfile.sh on Thu Jan 21 09:34:41 PST 2021
 ansicolors==1.1.8
 attrs==20.3.0
 beautifulsoup4==4.6.3
@@ -14,7 +14,6 @@ monotonic==1.5
 mypy==0.782
 mypy-extensions==0.4.3
 packaging==20.8
-pathspec==0.8.0
 pex==2.1.24
 pip==20.2.1
 pluggy==0.13.1
@@ -26,7 +25,7 @@ pyparsing==2.4.7
 pystache==0.5.4
 pytest==6.2.1
 python-dateutil==2.8.1
-PyYAML==5.3.1
+PyYAML==5.4.1
 requests==2.25.1
 setproctitle==1.2
 setuptools==50.3.2

3rdparty/python/requirements.txt

@@ -20,7 +20,7 @@ psutil==5.7.0
 pystache==0.5.4
 # This should be kept in sync with `pytest.py`.
 pytest>=6.0.1,<6.3
-PyYAML>=5.3.1,<5.4
+PyYAML>=5.4,<5.5
 requests[security]>=2.20.1
 setproctitle==1.2
 setuptools>=50.3.0,<50.4