Fix syntax highlighting in overview doc

[wjandrea]

Remove bogus syntax highlighting on LICENSE in overview.rst

I haven't really worked with RST myself, so please check my work.

• [ ] Closes # (insert issue number)
• Executed pre-commit run --all-files with no errors
• [ ] The change is fully covered by automated unit tests
• [ ] Documented in docs/ as appropriate
• [ ] Added an entry to the CHANGES file

[wjandrea]

link to readthedocs build: https://pint--2098.org.readthedocs.build/en/2098/getting/overview.html#license

[codspeed-hq]

CodSpeed Performance Report

Merging #2098 will not alter performance

_{Comparing wjandrea:patch-1 (ea61b7e) with master (415fcef)}

Summary

✅ 437 untouched benchmarks

[andrewgsavage]

looks better, thanks