Skip preview test on windows (firefox-devtools#5001)

Author: jasonLaster

src/test/mochitest/browser.ini

@@ -104,8 +104,9 @@ skip-if = os == "win"
 [browser_dbg-pretty-print-console.js]
 [browser_dbg-pretty-print-paused.js]
 [browser_dbg-preview.js]
-skip-if = true # regular failures during release in Bug 1415300
+skip-if = os == "win"
 [browser_dbg-preview-source-maps.js]
+skip-if = os == "win"
 [browser_dbg-returnvalues.js]
 [browser_dbg-scopes-mutations.js]
 [browser_dbg-search-file.js]