Update font.rst

I think the argument filename was from a previous version of the software for v1.18.14 it is no longer a kwarg, so it should be fontfile if I am not mistaken!

Author: inf3rnus

docs/font.rst

@@ -47,7 +47,7 @@ A Font object also contains useful general information, like the font bbox, the
 
          If you have installed `pymupdf-fonts <https://pypi.org/project/pymupdf-fonts/>`_, there are also new "reserved" fontnames available, which are listed in :attr:`fitz_fonts` and in the table further down.
 
-      :arg str filename: the filename of a fontfile somewhere on your system [#f1]_.
+      :arg str fontfile: the filename of a fontfile somewhere on your system [#f1]_.
       :arg bytes,bytearray,io.BytesIO fontbuffer: a fontfile loaded in memory [#f1]_.
       :arg in script: the number of a UCDN script. Currently supported in PyMuPDF are numbers 24, and 32 through 35.
       :arg str language: one of the values "zh-Hant" (traditional Chinese), "zh-Hans" (simplified Chinese), "ja" (Japanese) and "ko" (Korean). Otherwise, all ISO 639 codes from the subsets 1, 2, 3 and 5 are also possible, but are currently documentary only.