fix(i18n): enable the French translation of "Polygon"

The entry was flagged as fuzzy, so it was left out of the compiled
catalog and "Polygon" was shown untranslated in the French interface.

Assisted-by: Claude Opus 5.5

Author: PierreRaybaut

plotpy/locale/fr/LC_MESSAGES/plotpy.po

@@ -1489,7 +1489,6 @@ msgstr "Sélection"
 msgid "Polyline"
 msgstr "Ligne brisée"
 
-#, fuzzy
 msgid "Polygon"
 msgstr "Polygone"