Catch new SNMP errors in juniper alarm task

[johannaengland]

Scope and purpose

Fixes #212.

This amends the changes made in #231 according to the new SNMP errors introduced/handled in #262. This should finally lead to error being correctly handled and only things being logged if the device has an alarm count of an invalid type (but not none).

Contributor Checklist

• [X] Added a changelog fragment for towncrier
• [X] Linted/formatted the code with black, ruff and isort, easiest by using pre-commit
• [X] The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.04%. Comparing base (5d77dc6) to head (a6f6a89).

:exclamation: Current head a6f6a89 differs from pull request most recent head 5670e2b

Please upload reports for the commit 5670e2b to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #275 +/- ## ========================================== + Coverage 98.88% 99.04% +0.16% ========================================== Files 51 50 -1 Lines 6876 6776 -100 ========================================== - Hits 6799 6711 -88 + Misses 77 65 -12 ```

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