Fixing the flag boolean and the fixtures dir name

cabal-install/src/Distribution/Client/CmdConfigure.hs

@@ -106,7 +106,7 @@ configureAction' flags@NixStyleFlags {..} _extraArgs globalFlags = do
         appends = fromFlagOrDefault False $ configAppend configExFlags
         backupFile = localFile <> "~"
 
-    when (exists && not backups) $ do
+    when (exists && backups) $ do
       notice v $
         quote (takeFileName localFile) <> " already exists, backing it up to "
         <> quote (takeFileName backupFile) <> "."

cabal-install/tests/UnitTests/Distribution/Client/Configure.hs

@@ -97,4 +97,4 @@ configureTests = testGroup "Configure tests"
     ]
 
 projectFile :: FilePath
-projectFile = "tests" </> "fixtures" </> "reconfigure" </> "cabal.project"
+projectFile = "tests" </> "fixtures" </> "configure" </> "cabal.project"