fix: Add line breaks to error message

[cadonna]

Description

Adds line breaks to the error message when a schema is not found
as described in issue #7205.

Testing done

Adapted existing unit tests.

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

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[cadonna]

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