test: make cbus_call.test tap-compatible

NO_DOC=internal
NO_CHANGELOG=internal

test/unit/cbus_call.c

 #include "exception.h"
 #include "memory.h"
 #include "cbus.h"
+
+#define UNIT_TAP_COMPATIBLE 1
 #include "unit.h"
 
 static struct fiber *caller_fiber;

test/unit/cbus_call.result

-	*** main ***
-1..4
-ok 1 - cbus_call ordinary
-ok 2 - cbus_call timeout
-ok 3 - cbus_call wakeup
-ok 4 - cbus_call cancel
-	*** main: done ***