Upgrade certifi test dependency to fix security alert.

test_requirements.txt

@@ -2,7 +2,7 @@ appdirs==1.4.4; python_version >= '3.8'
 apprise==1.3.0
 attrs==22.2.0; python_version >= '3.8'
 black==23.3.0; python_version >= '3.8'
-certifi==2022.9.24
+certifi==2023.7.22
 chardet==5.1.0
 click==8.1.3; python_version >= '3.8'
 codespell==2.2.4