Update the message for client migration

[seppzer0]

Changelog: Fix: Update the message for client migration.
Docs: omit

• Refer to the issue that supports this Pull Request.
• If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
• I've read the Contributing guide.
• I've followed the PEP8 style guides for Python code.
• I've opened another PR in the Conan docs repo to the develop branch, documenting this one.

Fair note -- I did knowingly skip the discussion of this issue, because it subjectively seemed too trivial to discuss. Please let me know if you think otherwise.

In short, this is a simple fix of a string that gets shown in output when upgrading Conan version.
Additionally, a related f-string was converted into a regular string, since there's nothing to actually format for it.

[CLAassistant]

All committers have signed the CLA.

[memsharded]

Thanks for fixing this @seppzer0

Could you please check and sign the CLA? If you already tried and it didn't work, it can happen if the commit is signed with a different email rather than the Github email.

[seppzer0]

@memsharded , hi
Checked and signed the CLA, should be fine now

[memsharded]

Merged, thanks!, it will be in next 2.13