fix flake8 errors and add flake8 Github Action

[johanneskastl]

Add a GitHub action that lints the go_modules file.

[johanneskastl]

Only errors left:

go_modules:88:63: W605 invalid escape sequence '\.'
go_modules:88:90: W605 invalid escape sequence '\.'
go_modules:88:94: W605 invalid escape sequence '\.'

All from the big regex:

 87     basename = re.sub(                                                                                                                                                                   
 88         "^(?P<service_prefix>_service:[^:]+:)?(?P<basename>.*)\.(?P<extension>obscpio|tar\.[^\.]+)$",  # noqa: E501                                                                      
 89         r"\g<basename>",                                                                                                                                                                 
 90         archive_name,                                                                                                                                                                    
 91     )

[johanneskastl]

Only errors left:

go_modules:88:63: W605 invalid escape sequence '\.'
go_modules:88:90: W605 invalid escape sequence '\.'
go_modules:88:94: W605 invalid escape sequence '\.'

All from the big regex:

 87     basename = re.sub(                                                                                                                                                                   
 88         "^(?P<service_prefix>_service:[^:]+:)?(?P<basename>.*)\.(?P<extension>obscpio|tar\.[^\.]+)$",  # noqa: E501                                                                      
 89         r"\g<basename>",                                                                                                                                                                 
 90         archive_name,                                                                                                                                                                    
 91     )

This can be fixed by prepending a r:

-        "^(?P<service_prefix>_service:[^:]+:)?(?P<basename>.*)\.(?P<extension>obscpio|tar\.[^\.]+)$",  # noqa: E501
+        r"^(?P<service_prefix>_service:[^:]+:)?(?P<basename>.*)\.(?P<extension>obscpio|tar\.[^\.]+)$",  # noqa: E501

[johanneskastl]

Github Action for flake8 linting is now green :-)
https://github.com/johanneskastl/obs-service-go_modules/actions