patch 9.1.0636: filetype: ziggy files are not recognized

Problem:  filetype: ziggy files are not recognized
Solution: detect '*.ziggy' files as ziggy filetype,
          detect '*.ziggy-schema' files as ziggy-schema filetype
          (EliSauder)

References: https://ziggy-lang.io/

fixes: #15355
closes: #15367

Signed-off-by: EliSauder <24995216+EliSauder@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_filetype.vim

@@ -864,6 +864,8 @@ def s:GetFilenameChecks(): dict<list<string>>
     z8a: ['file.z8a'],
     zathurarc: ['zathurarc'],
     zig: ['file.zig', 'build.zig.zon'],
+    ziggy: ['file.ziggy'],
+    ziggy_schema: ['file.ziggy-schema'],
     zimbu: ['file.zu'],
     zimbutempl: ['file.zut'],
     zserio: ['file.zs'],