vim-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: vim/vim#14380

72d81a66ed

Co-authored-by: Wu, Zhenyu <wuzhenyu@ustc.edu>

test/old/testdir/test_filetype.vim

@@ -760,6 +760,7 @@ func s:GetFilenameChecks() abort
     \ 'yang': ['file.yang'],
     \ 'yuck': ['file.yuck'],
     \ 'z8a': ['file.z8a'],
+    \ 'zathurarc': ['zathurarc'],
     \ 'zig': ['file.zig', 'build.zig.zon'],
     \ 'zimbu': ['file.zu'],
     \ 'zimbutempl': ['file.zut'],