ci(release): debug .sig discovery, disable verify-nix during testing

- Replace the glob find for the .sig file with an explicit target-based
  path ($matrix → src-tauri/target/<target>-apple-darwin/release/bundle/
  macos/Psysonic.app.tar.gz.sig) and dump directory listings so we can
  see what tauri-action actually leaves behind if the path is wrong
- Skip verify-nix while we iterate fast on signing + updater (its auto-
  commits of flake.lock / npmDepsHash cause rebase friction on every
  release)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "Psysonic",
-  "version": "1.34.16",
+  "version": "1.34.17",
   "identifier": "dev.psysonic.player",
   "build": {
     "beforeDevCommand": "npm run dev",