LaTeX writer: fix fr-CA babel language mapping (#11576)

Map fr-CA to "french" instead of deprecated "canadien".

The babel-french package's `canadien.ldf` is deprecated and broken:
it never calls `\ldf@finish`, so `\bbl@main@language` is left undefined,
causing babel to crash at `\begin{document}`. Since `canadien` was always
just an unconditional alias for `french`, use `french` directly.

Closes #11575.

Author: cderv

src/Text/Pandoc/Writers/LaTeX/Lang.hs

@@ -40,7 +40,7 @@ toBabel (Lang "en" _ (Just "GB") _ _ _) = Just "british"
 toBabel (Lang "en" _ (Just "NZ") _ _ _) = Just "newzealand"
 toBabel (Lang "en" _ (Just "UK") _ _ _) = Just "british"
 toBabel (Lang "en" _ (Just "US") _ _ _) = Just "american"
-toBabel (Lang "fr" _ (Just "CA") _ _ _) = Just "canadien"
+toBabel (Lang "fr" _ (Just "CA") _ _ _) = Just "french"
 toBabel (Lang "fra" _ _ vars _ _)
   | "aca" `elem` vars                   = Just "acadian"
 toBabel (Lang "grc" _ _ _ _ _)          = Just "ancientgreek"