Clear Cocoapods cache before adding pod repo. (#789)

* Remove extraneous (?) pod repo add.

* Revert "Remove extraneous (?) pod repo add."

This reverts commit 67a3d3a.

* Clear cache.

* Whitespace.

Author: jonsimantov

.github/workflows/build_tvos.yml

@@ -108,7 +108,9 @@ jobs:
         shell: bash
         # The pod install fails during the cmake build, so preinstall it.
         run: |
+          rm -rf ~/Library/Caches/CocoaPods/* || true
           pod repo add cocoapods https://github.com/CocoaPods/Specs.git
+          pod repo update
 
       - id: unity_setup
         uses: ./gha/unity