Small fixes to flaky MoveIt Servo integration tests

[sea-bass]

Description

I've been seeing servo integration tests flake every now and then, and found it improved when removing the node before trying to cancel the executor and join its spinning thread.

I also changed some incorrect / characters in the integration test launch files' static transform publisher. We were failing to get a proper state from the planning scene because the virtual joint was flagged as missing.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
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