deps: bump WebKit to eb92990ae9e0a8df3141b8cf946a4f250393e213 (#21702)

## Summary
- Updates WebKit from 75f6499 to eb92990 (latest release from
oven-sh/webkit)
- This brings in the latest WebKit improvements and fixes

## Test plan
- [ ] Verify the build completes successfully
- [ ] Run existing test suite to ensure no regressions

🤖 Generated with [Claude Code](https://claude.ai/code)

---------

Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

cmake/tools/SetupWebKit.cmake

@@ -2,7 +2,7 @@ option(WEBKIT_VERSION "The version of WebKit to use")
 option(WEBKIT_LOCAL "If a local version of WebKit should be used instead of downloading")
 
 if(NOT WEBKIT_VERSION)
-  set(WEBKIT_VERSION 75f6499360f42d580c406f4969689a1e14b46447)
+  set(WEBKIT_VERSION 684d4551ce5f62683476409d7402424e0f6eafb5)
 endif()
 
 string(SUBSTRING ${WEBKIT_VERSION} 0 16 WEBKIT_VERSION_PREFIX)