Fix QlLinuxThreadManagement.threads to be updated appropriately

[vhertz]

Checklist

Which kind of PR do you create?

• This PR only contains minor fixes.
• This PR contains major feature update.
• This PR introduces a new function/api for Qiling Framework.

Coding convention?

• The new code conforms to Qiling Framework naming convention.
• The imports are arranged properly.
• Essential comments are added.
• The reference of the new code is pointed out.

Extra tests?

• No extra tests are needed for this PR.
• I have added enough tests for this PR.
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One last thing

• I have read the contribution guide

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As mentioned in #884, QlLinuxThreadManagement.threads is always empty. I have added the code to update this appropriately.

[xwings]

Thanks and welcome to Qiling Framework