libicudata.so as the name suggests is a DATA library. I doubt CET is applicable to that, or is it?

All shared libraries should be CET enabled.  GCC provides <cet.h> which can be included
in assembly codes to generate CET maker when compiling with -fcf-protection.

I created a pull request on github.  Can someone help me upstream it?

What do you mean by "help upstream it"? If you created a PR upstream that is already it, but you should watch the checks, specifically the one that says "Pull request title must start with a Jira ticket ID" and follow its Details link that effectively leads to http://site.icu-project.org/processes/contribute

(In reply to Eike Rathke from comment #4)
> What do you mean by "help upstream it"? If you created a PR upstream that is
> already it, but you should watch the checks, specifically the one that says
> "Pull request title must start with a Jira ticket ID" and follow its Details
> link that effectively leads to
> http://site.icu-project.org/processes/contribute

Pengfei, please help resolve this.

Hi Hongjiu,
  Thanks for your CET help and support!
  I already created one ICU JIRA https://unicode-org.atlassian.net/browse/CLDR-13646 to track this issue.
  And you could use this JIRA id to pull your request now.
  Thanks a lot!

Sorry, correct ICU JIRA https://unicode-org.atlassian.net/browse/ICU-21019 to track this issue.
Thanks!

This bug appears to have been reported against 'rawhide' during the Fedora 33 development cycle.
Changing version to 33.

Fixed as of icu 67.1.