Server manager `make test` always ends with an error

[edubart]

Context

make test always ends with an error and non 0 status code, despite success:

➜  make test FAST_TEST=true

Running tests:

GetVersion: . OK
HealthCheck: ..... OK
Session Simulations: .. OK
8 of 8 tests passed
make[1]: Entering directory '/home/bart/projects/cartesi/machine-emulator-sdk/server-manager/src'
make[1]: *** [Makefile:255: clean-test-processes] Terminated
make[1]: Leaving directory '/home/bart/projects/cartesi/machine-emulator-sdk/server-manager/src'
make: *** [Makefile:260: test] Error 2
➜ echo $?
2

Expected behavior

Exit status should be 0.