Fix global licensing being ignored with a .license file

[lineargraph]

Fixes https://github.com/fsfe/reuse-tool/issues/1057

• [x] Added a change log entry in changelog.d/<directory>/.
• [x] Added self to copyright blurb of touched files.
• [x] Added self to AUTHORS.rst.
• [x] Wrote tests.
• [ ] Documented my changes in docs/man/ or elsewhere. (n/a)
• [x] My changes do not contradict the current specification.
• [x] I agree to license my contribution under the licenses indicated in the changed files.