[acceptance] Bug: wrong exit-code in CI for runtime errors

[scharissis]

Works locally, but not in CI.

=== Failed
=== FAIL: cmd TestExitCodeBehavior/Runtime_error_should_exit_with_code_2 (0.09s)
    main_test.go:225: Running op-acceptor with testdir=/tmp/op-acceptor-test-1287960304/non-existent-dir, gate=test-gate-passes, validators=/tmp/op-acceptor-test-1287960304/test-validators.yaml
    main_test.go:236: Exit code: 1
    main_test.go:121: 
                Error Trace:    /root/project/op-acceptor/cmd/main_test.go:121
                Error:          Not equal: 
                                expected: 2
                                actual  : 1
                Test:           TestExitCodeBehavior/Runtime_error_should_exit_with_code_2
                Messages:       Unexpected exit code

=== FAIL: cmd TestExitCodeBehavior (8.50s)