Update firebase deploy script to latest from firebase CLI

Generated with firebase init hosting:github

I'm hoping this will fix my errors with pull requests not having access to the
secret key, maybe? But I don't know how it would. I'm just ruling it out at
this stage that there's no fix by updating.

.github/workflows/firebase-hosting-merge.yml

@@ -19,5 +19,3 @@ jobs:
           firebaseServiceAccount: '${{ secrets.FIREBASE_SERVICE_ACCOUNT_NZWIRELESSMAP_FIREBASE }}'
           channelId: live
           projectId: nzwirelessmap-firebase
-        env:
-          FIREBASE_CLI_PREVIEWS: hostingchannels

.github/workflows/firebase-hosting-pull-request.yml

@@ -3,8 +3,13 @@
 
 name: Deploy to Firebase Hosting on PR
 'on': pull_request
+permissions:
+  checks: write
+  contents: read
+  pull-requests: write
 jobs:
   build_and_preview:
+    if: '${{ github.event.pull_request.head.repo.full_name == github.repository }}'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
@@ -15,5 +20,3 @@ jobs:
           repoToken: '${{ secrets.GITHUB_TOKEN }}'
           firebaseServiceAccount: '${{ secrets.FIREBASE_SERVICE_ACCOUNT_NZWIRELESSMAP_FIREBASE }}'
           projectId: nzwirelessmap-firebase
-        env:
-          FIREBASE_CLI_PREVIEWS: hostingchannels