Add test for writable permission on REPO_DIR

tests/conda/repo-path/verify

@@ -13,5 +13,8 @@ assert sys.executable.startswith("/srv/conda/"), sys.executable
 assert os.path.exists("/srv/repo/verify")
 assert os.path.abspath(__file__) == "/srv/repo/verify"
 
+# Repo should be writable
+assert os.access("/srv/repo", os.W_OK)
+
 # We should be able to import the package in environment.yml
 import numpy