DDST-923 : Fixing spreadsheet ingest form states.

[MorganDawe]

No description provided.

[nchiasson-dgi]

Linting error that occurs is:

FILE: ...est/islandora_spreadsheet_ingest/src/Plugin/migrate/source/Spreadsheet.php
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FOUND 1 ERROR AFFECTING 1 LINE
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 104 | ERROR | [x] Parameter $migration has null default value, but is not
     |       |     marked as nullable.
     |       |     (SlevomatCodingStandard.TypeHints.NullableTypeForNullDefaultValue.NullabilityTypeMissing)
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PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
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Which isn't part of the work being completed above, but can be addressed separately.