Use i386 images for i386 jobs

.gitlab/gen_ci.hs

@@ -171,9 +171,12 @@ archName I386  = "i386"
 -- The path to the docker image (just for linux builders)
 dockerImage :: Arch -> Opsys -> Maybe String
 dockerImage arch (Linux distro) =
-    Just image
+    Just (archStr ++ image)
   where
     image = distroName distro
+    archStr = case arch of
+      I386 -> "i386/"
+      _ -> ""
 dockerImage _ _ = Nothing
 
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