[chore](github) Optimize BE UT workflows

[adonis0147]

Proposed changes

Issue Number: close #xxx

Problem summary

In #14533 , we run BE UT workflows periodically to share the cache with brand new pull requests. However, we don't need to save the cache when the unit tests doesn't run, otherwise it may occupy huge cache space and some useful caches will be evicted by GitHub.

Checklist(Required)

1. Does it affect the original behavior:
   • Yes
   • No
   • I don't know
2. Has unit tests been added:
   • Yes
   • No
   • No Need
3. Has document been added or modified:
   • Yes
   • No
   • No Need
4. Does it need to update dependencies:
   • Yes
   • No
5. Are there any changes that cannot be rolled back:
   • Yes (If Yes, please explain WHY)
   • No

Further comments

If this is a relatively large or complex change, kick off the discussion at dev@doris.apache.org by explaining why you chose the solution you did and what alternatives you considered, etc...

[morningman]

LGTM

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.

[hello-stephen]

TeamCity pipeline, clickbench performance test result:
the sum of best hot time: 36.41 seconds
load time: 460 seconds
storage size: 17170601959 Bytes
https://doris-community-test-1308700295.cos.ap-hongkong.myqcloud.com/tmp/20221124163539_clickbench_pr_52554.html