qa-tests: targeting test-runners with labels, detecting test completion, increasing workflow timeout

[mriccobene]

This pull request introduces several enhancements:

• It specifies in the test workflow that commits on the main or release/3.x branches should be executed on the test-runner labeled Erigon3.
• It enhances the detection of test completion, and will skip uploading test results if they are incomplete, thus avoiding erroneous error signals during the upload process.
• It improves the directory cleanup process
• It increases the workflow timeout (which is 6 hours by default but can be increased to 35 days on self-hosted runners)