Added CompoundIdentifier class is_input_header negative test

[musasizivictoria]

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• Have you written new tests for your core changes, as applicable?
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Description
Added negative tests for the is_input_header method in the CompoundIdentifier class. These tests ensure that invalid headers are correctly identified by the method and return False.

Changes to be made

1. Implement negative tests to check the method's behavior for invalid headers

Status

• Implemented and successfully ran negative tests locally with all tests passing

To do

• Review and ensure code coverage
• Continue with further unit tests for other methods of the CompoundIdentifier class

Is this pull request related to any open issue? If yes, replace issueID below with the issue ID

Related to #

[DhanshreeA]

@musasizivictoria could you please resolve conflicts? Thanks!

[musasizivictoria]

am sorry @DhanshreeA it seems we are working on same TEST many people

[DhanshreeA]

@musasizivictoria could you please take care of the conflicts?

[musasizivictoria]

@musasizivictoria could you please take care of the conflicts?

Addressed, thanks @DhanshreeA

[musasizivictoria]

Also some clarity here if you don't mind
#1319 (comment)