Move `test_runtime.py` out of test folder

[tobitege]

The test_runtime.py, which started as a unit test, is now run in a special workflow and explicitly excluded from unit tests workflow.

Suggested actions:

• move the file into a different folder (and/or rename it)
• adapt its call in ghcr_runtime workflow accordingly:

https://github.com/All-Hands-AI/OpenHands/blob/a7dfd5b9facc5726369152d10853c99df3c5c88e/.github/workflows/ghcr_runtime.yml#L194

• adapt unit test workflows to remove occurences of -k "not test_runtime.py": https://github.com/All-Hands-AI/OpenHands/blob/a7dfd5b9facc5726369152d10853c99df3c5c88e/.github/workflows/py-unit-tests.yml#L85

https://github.com/All-Hands-AI/OpenHands/blob/a7dfd5b9facc5726369152d10853c99df3c5c88e/.github/workflows/py-unit-tests.yml#L114

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@xingyaoww wrote: "@tobitege on a second note, we should probably move test_runtime out of that directory and break it down to multiple files to avoid similar confusions in the future 😄

Originally posted by @xingyaoww in https://github.com/All-Hands-AI/OpenHands/issues/3464#issuecomment-2299181355