Fix trigger of fetcher tests

[koppor]

Follow-up to #8258 -> org.jabref.logic.importer.fileformat.pdf.PdfMergeMetadataImporterTest is marked as fetcher test. Thus, fetcher tests should run if a change in this file occurs.

Whole thing triggered by #12088 rendering a test not working, but did not show up, because no fetcher tests ran.

Mandatory checks

• I own the copyright of the code submitted and I licence it under the MIT license
• Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[InAnYan]

I was thinking: what about adding whole importer/**? Importers != fetchers?

[koppor]

• importers work on the local file system
• fetchers work on remoate
• PdfMergeMetaDataImporter is a "hybrid", because it works on the file system, but also uses external sourfces

Aim of having less triggers: Not hitting any rate limit.

[koppor]

Not sure where to note that down? package-info.java in package org.jabref.logic.importer.fetcher?

[github-actions]

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