fix closeAwaitTermination UT

[marsishandsome]

What problem does this PR solve?

The UT of session.closeAwaitTermination is not stable, because it depends on time.

What is changed and how it works?

remove the time from the UT.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to be included in the release note

[marsishandsome]

/run-all-tests

[birdstorm]

LGTM