Adding DLLs to cardano-launcher:unit on windows

This should hopefully ensure Moritz's fix also applies to the
cardano-launcher:unit failure.

> 002a:err:module:import_dll Library libstdc++-6.dll (which is needed by L"Z:\\nix\\store\\51vhwb1fdckhx4xiammryf97ip8m3h9d-cardano-wallet-launcher-test-unit-x86_64-w64-mingw32-2021.6.11\\bin\\unit.exe") not found
> 002a:err:module:attach_dlls Importing dlls for L"Z:\\nix\\store\\51vhwb1fdckhx4xiammryf97ip8m3h9d-cardano-wallet-launcher-test-unit-x86_64-w64-mingw32-2021.6.11\\bin\\unit.exe" failed, status c0000135
> builder for '/nix/store/7ssdwhn0gani60q7pwkw13aavbm4ygw1-cardano-wallet-launcher-test-unit-x86_64-w64-mingw32-2021.6.11-check-x86_64-w64-mingw32.drv' failed with exit code 53

nix/haskell.nix

@@ -185,6 +185,7 @@ let
         packages.cardano-wallet.components.exes.cardano-wallet.postInstall = optparseCompletionPostInstall + libSodiumPostInstall;
         packages.cardano-wallet-core.components.tests.unit.postInstall = libSodiumPostInstall;
         packages.cardano-wallet-cli.components.tests.unit.postInstall = libSodiumPostInstall;
+        packages.cardano-wallet-launcher.components.tests.unit.postInstall = libSodiumPostInstall;
       })
 
       ({ config, ...}: let