vim-patch:9.1.1548: filetype: OpenFGA files are not recognized

Problem:  filetype: OpenFGA files are not recognized
Solution: detect *.fga files as fga filetype, include an fga filetype
          plugin (Riley Bruins)

References:
https://github.com/openfga
https://marketplace.visualstudio.com/items?itemName=openfga.openfga-vscode

closes: vim/vim#17752

0992f62fc1

Co-authored-by: Riley Bruins <ribru17@hotmail.com>

test/old/testdir/test_filetype.vim

@@ -285,6 +285,7 @@ func s:GetFilenameChecks() abort
     \ 'faust': ['file.dsp', 'file.lib'],
     \ 'fennel': ['file.fnl', '.fennelrc', 'fennelrc'],
     \ 'fetchmail': ['.fetchmailrc'],
+    \ 'fga': ['file.fga'],
     \ 'fgl': ['file.4gl', 'file.4gh', 'file.m4gl'],
     \ 'firrtl': ['file.fir'],
     \ 'fish': ['file.fish'],