[libs] Bumping PyYaml to 5.4.1 in Python 3

desktop/core/requirements.txt

@@ -55,7 +55,7 @@ python-ldap==3.1.0
 python-oauth2==1.1.0
 pytidylib==0.3.2
 pytz==2021.1
-pyyaml>=4.2b1
+PyYAML==5.4.1
 requests>=2.25.1
 requests-kerberos==0.12.0
 rsa==4.7