Add check for KeyError on reading plugin commit

[LavissaWoW]

Closes #6286

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[LavissaWoW]

@SchrodingersGat Only fails in Postgres CI, and passes fine locally. Ideas?

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ERROR: test_invalid_barcode (plugin.base.barcodes.test_barcode.SOAllocateTest)
Test when an invalid barcode is provided (does not match stock item).
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Traceback (most recent call last):
  File "/home/runner/work/InvenTree/InvenTree/InvenTree/plugin/base/barcodes/test_barcode.py", line 312, in test_invalid_barcode
    item.part.assign_barcode(barcode_data='abcde')
  File "/home/runner/work/InvenTree/InvenTree/InvenTree/InvenTree/models.py", line 1051, in assign_barcode
    self.save()
  File "/home/runner/work/InvenTree/InvenTree/InvenTree/part/models.py", line 474, in save
    self.full_clean()
  File "/opt/hostedtoolcache/Python/3.9.18/x64/lib/python3.9/site-packages/django/db/models/base.py", line 1251, in full_clean
    raise ValidationError(errors)
django.core.exceptions.ValidationError: {'variant_of': ['Part instance with id 10003 does not exist.']}

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[SchrodingersGat]

This looks like an error with the test fixtures. Sometimes if you change the order of operations of tests, the fixture data is "corrupt" - especially for postgres which is a lot stricter. No idea why your change would cause an error here.

In the part.yaml fixture, try adding is_template=true to part with pk=10003:

InvenTree/InvenTree/part/fixtures/part.yaml

Line 183 in c5d0902

variant_of: 10000