[deep link] Update loading string

Pre-launch Checklist

[ ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
[ ] I read the Tree Hygiene wiki page, which explains my responsibilities.
[ ] I read the Flutter Style Guide recently, and have followed its advice.
[ ] I signed the CLA.
[ ] I listed at least one issue that this PR fixes in the description above.
[ ] I updated/added relevant documentation (doc comments with ///).
[ ] I added new tests to check the change I am making, or there is a reason for not adding tests.

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