Warn when nix package version is set unnecessarily

The README used to recommend overriding `version = shortRev`, however we
now use `shortRev` by default.

Notify users of this change by warning when `version` is overridden to
the version we would've used anyway.

packaging/nix/package.nix

@@ -29,6 +29,7 @@
     # Warnings added in https://github.com/Open-Wine-Components/umu-launcher/pull/345 (2025-01-27)
     lib.warnIf (args ? truststore) "umu-launcher: the argument `truststore` has been renamed to `withTruststore`."
     lib.warnIf (args ? cbor2) "umu-launcher: the argument `cbor2` has never had any effect. The new argument `withDeltaUpdates` should be used instead."
+    lib.warnIf (version == umu-launcher-unwrapped.version) "umu-launcher: the argument `version` is no longer necessary. The version now uses `shortRev` by default."
     lib.optionalAttrs (args ? version) {inherit version;}
     // lib.optionalAttrs (args ? withTruststore || args ? truststore) {inherit withTruststore;}
     // lib.optionalAttrs (args ? withDeltaUpdates) {inherit withDeltaUpdates;};