Integrate gutenberg-mobile release 1.42.1 (fix)

[aforcier]

This is a follow-up to #13540, using the right gutenberg-mobile tag for release 1.42.1.

As far as I can tell, #13540 was tested with the right branch, but this final commit updating to the release tag hash accidentally used the tag for 1.42.0 instead of 1.42.1.

Comparing the previous tag in that PR (that it was tested with) to the one I'm using in this PR, you can see the change is only the tag update:

wordpress-mobile/gutenberg-mobile@3000ec...5d7a4d2

And that release/16.3 without this PR is actually incorrectly pointing to gutenberg-mobile 1.42.0:

https://github.com/wordpress-mobile/gutenberg-mobile/releases/tag/v1.42.0 (see that the hash is 6fed9e)

To test:

Should have already been tested in #13540, just check that this builds.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APK here.

[cameronvoell]

Verified the commit hash and the story post icon fix. Thanks for catching this Alex!