patch 9.1.1501: filetype: flix files are not recognized

Problem:  filetype: flix files are not recognized
Solution: detect *.flix files as flix filetype
          (0xadk)

References:
- https://flix.dev/
- https://doc.flix.dev/introduction.html

closes: #17646

Signed-off-by: 0xadk <0xadk@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/filetype.vim

@@ -893,6 +893,9 @@ au BufNewFile,BufRead *.fish			setf fish
 " Flatpak config
 au BufNewFile,BufRead */flatpak/repo/config	setf dosini
 
+" Flix
+au BufNewFile,BufRead *.flix			setf flix
+
 " Focus Executable
 au BufNewFile,BufRead *.fex,*.focexec		setf focexec
 

src/testdir/test_filetype.vim

@@ -287,6 +287,7 @@ def s:GetFilenameChecks(): dict<list<string>>
     fgl: ['file.4gl', 'file.4gh', 'file.m4gl'],
     firrtl: ['file.fir'],
     fish: ['file.fish'],
+    flix: ['file.flix'],
     focexec: ['file.fex', 'file.focexec'],
     form: ['file.frm'],
     forth: ['file.ft', 'file.fth', 'file.4th'],

src/version.c

@@ -719,6 +719,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1501,
 /**/
     1500,
 /**/