[DPE-6042] Quote tox.ini repository paths (#678)

Author: sinclert-canonical

tox.ini

@@ -6,13 +6,13 @@ no_package = True
 env_list = lint, unit
 
 [vars]
-src_path = {tox_root}/src
-tests_path = {tox_root}/tests
+src_path = "{tox_root}/src"
+tests_path = "{tox_root}/tests"
 all_path = {[vars]src_path} {[vars]tests_path}
 
 [testenv]
 set_env =
-    PYTHONPATH = {tox_root}/lib:{[vars]src_path}
+    PYTHONPATH = {tox_root}/lib:{tox_root}/src
     PY_COLORS = 1
 allowlist_externals =
     poetry