tectonic: Update checkver

[aliesbelik]

From Excavator logs:

tectonic: couldn't match 'releases/tag/tectonic%40([\d.]+)' in https://github.com/tectonic-typesetting/tectonic/releases

• [x] I have read the Contributing Guide.

[aliesbelik]

/verify

[github-actions[bot]]

All changes look good.

Wait for review from human collaborators.

tectonic

• [x] Description
• [x] License
• [x] Hashes
• [x] Checkver
• [x] Autoupdate

[aliesbelik]

Updated to 0.15.0 but still in Excavator logs:

tectonic: couldn't match 'releases/tag/tectonic%40([\d.]+)' in https://github.com/tectonic-typesetting/tectonic/releases