False positive on template files named like the thumbnail

[elegaanz]

If a file in the template has the same base name as the thumbnail, it will raise an error. See the annotation on this file: https://github.com/typst/packages/pull/4951/changes#diff-035a421521ea66d1a47b094482a1f2a94753dfd9730182174526c8ad87bb84f7

[saecki]

This is actually not a false positive, but a bug in the bundler, and the package-check just matches that behavior. The thumbnail path is added to the ignore::Override and since most of the time it's not an absolute path and just a filename, it will match all other files with the same name.
When adding it to the override, we should make sure that it's always an absolute path from the package root.