Fix upgradeGHCup

File needs to be unlinked first, because it might
potentially be in use.

lib/GHCup.hs

@@ -697,10 +697,15 @@ upgradeGHCup dls mtarget = do
   case mtarget of
     Nothing -> do
       dest <- liftIO $ ghcupBinDir
+      liftIO $ hideError NoSuchThing $ deleteFile (dest </> fn)
       handleIO (throwE . CopyError . show) $ liftIO $ copyFile p
                                                                (dest </> fn)
                                                                Overwrite
-    Just fullDest -> liftIO $ copyFile p fullDest Overwrite
+    Just fullDest -> do
+      liftIO $ hideError NoSuchThing $ deleteFile fullDest
+      handleIO (throwE . CopyError . show) $ liftIO $ copyFile p
+                                                               fullDest
+                                                               Overwrite
   pure latestVer