Added permissions for GitHub workflow config

[aalej]

Description

Fixes #6789

Issue above describes that there are missing permissions when a GitHub action workflow is triggered. See this Stack Overflow post. Adding the permissions in the yaml file should resolve the issue.

Scenarios Tested

1. Run firebase init hosting --project <project_id>
   • Yes to all defaults
2. Run firebase init hosting:github
   • Log in to GitHub
   • Enter your GitHub repository
   • Select all defaults
3. Push to the repository

git init
git add .
git commit -m "first commit"
git branch -M main
git remote add origin https://github.com/<repo>
git push -u origin main

4. Create a new PR. Do the ff:
   • Run git branch some-branch
   • Run git switch some-branch
   • Make changes to some files
   • Push the changes to a remote branch:

git add .
git commit -m "some branch changes"
git push origin some-branch

5. Submit the PR
   • “Deploy to Firebase Hosting on PR / build_and_preview (pull_request)” should be successful

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (09c2641) 54.30% compared to head (65a5658) 54.30%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6791   +/-   ##
=======================================
  Coverage   54.30%   54.30%           
=======================================
  Files         350      350           
  Lines       24301    24301           
  Branches     5029     5029           
=======================================
  Hits        13196    13196           
  Misses       9899     9899           
  Partials     1206     1206           

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