[FR] Fix handling non-numeric values from the 'Unité' template

[BoboTiG]

• Wiktionary page: https://fr.wiktionary.org/wiki/couteau_d%E2%80%99office

Wikicode:

{{Unité|8 à 12|cm}}

Output:

  File "lang/fr/template_handlers.py", line 966, in render_unite
    phrase = number(parts.pop(0), float_separator, thousands_separator)
  File "user_functions.py", line 354, in number
    res = f"{float(number):,}"
ValueError: could not convert string to float: '8à12'

Expected:

8 à 12 cm

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Model link, if any: https://fr.wiktionary.org/wiki/Mod%C3%A8le:Unit%C3%A9