Update dependency python-dotenv to v0.21.0

Author: renovate[bot]

requirements.txt

@@ -4,7 +4,7 @@ deprecated==1.2.13; python_version >= "3.6" and python_full_version < "3.0.0" or
 loguru==0.6.0; python_version >= "3.5"
 packaging==21.3; python_version >= "3.6"
 pyparsing==3.0.8; python_full_version >= "3.6.8" and python_version >= "3.6"
-python-dotenv==0.20.0; python_version >= "3.5"
+python-dotenv==0.21.0; python_version >= "3.5"
 redis==4.2.2; python_version >= "3.6"
 win32-setctime==1.1.0; sys_platform == "win32" and python_version >= "3.5"
 wrapt==1.14.0; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"