[Backport 2.x] Update backport CI, add PR merged condition

[ps48]

Description

Update backport CI, add PR merged condition #226

Issues Resolved

[List any issues this PR will resolve]

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[codecov]

Codecov Report

Merging #228 (3bf5dae) into 2.x (556e8b8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              2.x     #228   +/-   ##
=======================================
  Coverage   94.73%   94.73%           
=======================================
  Files           5        5           
  Lines         152      152           
  Branches       45       45           
=======================================
  Hits          144      144           
  Misses          8        8