patch 9.1.0278: filetype: zathurarc files not recognized

Problem:  filetype: zathurarc files not recognized
Solution: Detect '.zathurarc' files as zathurarc filetype,
          add zathurarc filetype (Wu, Zhenyu)

closes: #14380

Signed-off-by: Wu, Zhenyu <wuzhenyu@ustc.edu>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_filetype.vim

@@ -827,6 +827,7 @@ def s:GetFilenameChecks(): dict<list<string>>
     yang: ['file.yang'],
     yuck: ['file.yuck'],
     z8a: ['file.z8a'],
+    zathurarc: ['zathurarc'],
     zig: ['file.zig', 'build.zig.zon'],
     zimbu: ['file.zu'],
     zimbutempl: ['file.zut'],

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    278,
 /**/
     277,
 /**/