[lldb][test] skip Lua tests when the Lua interpreter is not found

When Swig is installed but not any Lua interpreter, the cmake script in
`lldb/cmake/modules/FindLuaAndSwig.cmake` will execute
`find_program(LUA_EXECUTABLE, ...)` and this will set the `LUA_EXECUTABLE`
variable to `LUA_EXECUTABLE-NOTFOUND`.

Ensure that in this case we are skipping the Lua tests requiring the
interpreter.

Author: vpalatin

lldb/test/API/lua_api/TestLuaAPI.py

@@ -158,7 +158,11 @@ def get_tests(self):
         return tests
 
     def test_lua_api(self):
-        if "LUA_EXECUTABLE" not in os.environ or len(os.environ["LUA_EXECUTABLE"]) == 0:
+        if (
+            "LUA_EXECUTABLE" not in os.environ
+            or len(os.environ["LUA_EXECUTABLE"]) == 0
+            or "NOTFOUND" in os.environ["LUA_EXECUTABLE"]
+        ):
             self.skipTest("Lua API tests could not find Lua executable.")
             return
         lua_executable = os.environ["LUA_EXECUTABLE"]