Change log level from info to error on request failure

[brianstrauch]

Use ERROR level when log starts with "Request {request_id} failed". Match the other two occurrences of this pattern:

• skypilot/sky/server/requests/executor.py

  Lines 255 to 257 in ddef9a5

  	logger.error(
  	f'Request {request_id} failed to get processed '
  	f'{common_utils.format_exception(e, use_bracket=True)}')

• skypilot/sky/server/requests/executor.py

  Lines 661 to 662 in ddef9a5

  	logger.error(f'Request {request_id} failed due to '
  	f'{common_utils.format_exception(e)}')

Tested (run the relevant ones):

• Code formatting: install pre-commit (auto-check on commit) or bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: /smoke-test (CI) or pytest tests/test_smoke.py (local)
• Relevant individual tests: /smoke-test -k test_name (CI) or pytest tests/test_smoke.py::test_name (local)
• Backward compatibility: /quicktest-core (CI) or pytest tests/smoke_tests/test_backward_compat.py (local)