test: mask-editor screenshot tolerance applied to one of two same-locator captures

Nit from reviewing #16669 (merged), filed as an issue per the agreed nit rule.

`browser_tests/tests/maskEditor.spec.ts` captures the same `.mask-editor-dialog` locator twice: `:165-168` (context-menu path) now carries `maxDiffPixels: 25`, while `:134` (open path) has no tolerance. The open-path capture sits behind a heavier settle sequence and has not been observed flaking, so this is hardening, not a defect: if `:134` ever shows the same 13 to 16px raster noise, 25 is the number.