Update build.yml (#520)

## All PRs:

* [x] Has tests N/A
* [x] Documentation updated N/A

## Adding a new header

Generally, adding a new header is always OK.

* Is the header supported by any user agent? If so, which?
* What does it do?
* What are the valid values for the header?
* Where does the specification live?

## Adding a new CSP directive

* Is the directive supported by any user agent? If so, which?
* What does it do?
* What are the valid values for the directive?

---------

Co-authored-by: Rahul Zhade <[email protected]>

Author: boveus

.github/workflows/build.yml

@@ -15,10 +15,8 @@ jobs:
       uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
     - name: Build and test with Rake
       run: |
-        gem install bundler
-        bundle install --jobs 4 --retry 3 --without guard
-        bundle exec rspec spec
         bundle exec rubocop
-
+        bundle exec rspec spec