tmp: pin GutenbergKit to PR #554 to verify source maps

TEMPORARY — do not merge. Pins GutenbergKit to its `pr-build/554` snapshot
branch so a prototype build consumes the PR build's XCFramework (which contains
an intentional test exception) and its published source maps. Revert to
`from: "0.17.2"` before merging.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dcalhoun

Modules/Package.resolved

@@ -60,7 +60,10 @@ let package = Package(
             revision: "b34794c9a3f32312e1593d4a3d120572afa0d010"
         ),
         .package(url: "https://github.com/zendesk/support_sdk_ios", from: "8.0.3"),
-        .package(url: "https://github.com/wordpress-mobile/GutenbergKit", from: "0.17.2"),
+        // TEMPORARY: pin to GutenbergKit PR #554's snapshot branch to verify
+        // Sentry source-map symbolication end to end. Revert to `from: "0.17.2"`
+        // before merging.
+        .package(url: "https://github.com/wordpress-mobile/GutenbergKit", branch: "pr-build/554"),
         .package(
             url: "https://github.com/automattic/wordpress-rs",
             exact: "0.4.0"