Move webkit-mask-box-enumeration.html into compat/ (#35927)

This was accidentally added to the root directory here:
https://github.com/web-platform-tests/wpt/pull/34520
diff --git a/webkit-mask-box-enumeration.html b/compat/webkit-mask-box-enumeration.html
similarity index 100%
rename from webkit-mask-box-enumeration.html
rename to compat/webkit-mask-box-enumeration.html