Entry macro doesn't use correct conditional compilation logic to call start test

[corwinkuiper]

If in test mode, it calls agb::test_runner::agb_start_tests. Two issues:

• I can define something called agb myself and break this.
• test_runner is only defined with the testing feature (in test mode dependencies are not compiled in test mode), so this macro fails to work with rust analyzer on projects that don't use the testing feature (eg. Hyperspace Roll) as rust analyzer does use test.