fix(main.yml): change private key password name

Tauri's documentation/support for their GitHub actions script is
really bad...

Ref: https://v2.tauri.app/plugin/updater/

.github/workflows/main.yml

@@ -49,7 +49,7 @@ jobs:
               env:
                   GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
                   TAURI_SIGNING_PRIVATE_KEY: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY }}
-                  TAURI_KEY_PASSWORD: ${{ secrets.TAURI_KEY_PASSWORD }}
+                  TAURI_SIGNING_PRIVATE_KEY_PASSWORD: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY_PASSWORD }}
               with:
                   tagName: v__VERSION__ # the action automatically replaces \_\_VERSION\_\_ with the app version.
                   releaseName: "Release v__VERSION__"