ci: Run pod lib lint in parallel (#2255)

Pod lib lint runs validations for all platforms sequentially. We can
speed up CI by using a matrix for each platform, so
they run in parallel.

.github/workflows/lint.yml

@@ -43,11 +43,15 @@ jobs:
  validate-podspec:
  name: Validate Podspec
  runs-on: macos-12
+ strategy:
+ matrix:
+ platform: ['ios', 'macos', 'tvos', 'watchos']
+
  steps:
  - uses: actions/checkout@v3
  - run: ./scripts/ci-select-xcode.sh
  - name: Validate Podspec
- run: pod lib lint --verbose
+ run: pod lib lint --verbose --platforms=${{ matrix.platform }}
  shell: sh
 
  validate-high-risk-files: