NAT-328: fixed tox issues

test/conftest.py

@@ -60,7 +60,7 @@ class FakerProvider(BaseProvider):
         return self.generator.numerify("SID-#####")
 
     def site_name(self) -> str:
-        site_name = ''.join(self.generator.random_letter().upper() for _ in range(3))
+        site_name = "".join(self.generator.random_letter().upper() for _ in range(3))
 
         if self.generator.boolean():
             digit = self.generator.random_int(min=1, max=9)