Fail to parse lintian tag M:

Debexpo importer fail to parse lintian M: severity tags.

Log:

Plugin lintian failed: Traceback (most recent call last):
  File "/var/www/debexpo/debexpo/plugins/models.py", line 130, in run 
    plugin.run(changes, source)
  File "/var/www/debexpo/debexpo/plugins/lintian.py", line 109, in run 
    severity = f'{severity}-{self.levels[severity]["name"]}'
KeyError: 'M' 
[2022-08-18 04:20:59,766: WARNING/ForkPoolWorker-2] Plugin lintian failed: Traceback (most recent call last):
  File "/var/www/debexpo/debexpo/plugins/models.py", line 130, in run 
    plugin.run(changes, source)
  File "/var/www/debexpo/debexpo/plugins/lintian.py", line 109, in run 
    severity = f'{severity}-{self.levels[severity]["name"]}'
KeyError: 'M' 

M: seems to have something to do with hint's masks), which is computed from screens which is an field from tags tied to a module.

I have tried to replicate the issue on the affected .dsc package, without success. It might be triggered by something else in the upload (.changes?) or by the way we run lintian on mentors.

Note that the fail does not prevent the importer from succeeding.