twister: Look at SIMICS_PROJECT environment variable to find simics

While cmake/emu/simics.cmake uses SIMICS_PROJECT env var, twister checks
if a build is "runnable" by checking if `simics` is executable, but it
doesn't look at SIMICS_PROJECT env var.

Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>

scripts/pylib/twister/twisterlib/platform.py

@@ -30,6 +30,9 @@ class Simulator:
         self.exec = data.get("exec")
 
     def is_runnable(self) -> bool:
+        if self.name == "simics":
+            return shutil.which(self.exec, path=os.environ.get("SIMICS_PROJECT")) is not None
+
         return not bool(self.exec) or bool(shutil.which(self.exec))
 
     def __str__(self):