fix: update GitHub Actions workflow to use 'main' branch for web-flasher checkout instead of version input

.github/workflows/custom_build.yml

@@ -56,7 +56,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: meshtastic/web-flasher
-          ref: ${{ inputs.version }}
+          ref: main
           path: web-flasher
           submodules: recursive
           fetch-depth: 1