Update Gutenberg ref

[derekblank]

Updates Gutenberg ref to latest from trunk to prevent the CI Pipeline Upload task from reporting not our ref, currently blocking the 1.102.0 release:

[2023-08-18T04:02:47Z] From github.com:wordpress-mobile/gutenberg-mobile
[2023-08-18T04:02:47Z]  * branch              refs/pull/6085/head -> FETCH_HEAD
[2023-08-18T04:02:47Z] Fetching submodule gutenberg
[2023-08-18T04:02:47Z] From github.com:WordPress/gutenberg
[2023-08-18T04:02:47Z]  = [up to date]            trunk      -> origin/trunk
[2023-08-18T04:02:49Z] fatal: remote error: upload-pack: not our ref 62dd7816cfc387aaaf1fa0d51f8820cb4be5a6b3
[2023-08-18T04:02:49Z] Errors during submodule fetch:
[2023-08-18T04:02:49Z] 	gutenberg
[2023-08-18T04:02:49Z] ⚠️ Warning: Checkout failed! exit status 1 (Attempt 2/3 Retrying in -2.650912691s)
[2023-08-18T04:02:49Z] 🚨 Error: exit status 1

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes more info and have added them to RELEASE-NOTES.txt if necessary.

[derekblank]

Closing, resolved by #6089