Add workflow that builds tvOS (#484)

Fixed up workflow to build Unity for tvOS targets.

Workflow is triggered by manual triggers still - and not by the `Firebase Unity SDK build` which kicks-off builds for all of the platforms. This is simply so we don't release the tvOS libraries. Later, when the tvOS release is ready, we'll add this `Build tvOS (SubWorkflow)` to the main build list.

Author: DellaBitta

.github/workflows/build_tvos.yml

@@ -3,7 +3,7 @@ name: Build tvOS (SubWorkflow)
 
 on:
   workflow_dispatch:
-  inputs:
+    inputs:
       unity_version:
         description: 'Unity version'
         default: '2019'
@@ -25,7 +25,7 @@ on:
         type: string
       unity_platform_name:
         description: 'The platform name Unity should install with'
-        default: 'tvOS'
+        default: 'tvOS,iOS'
         required: true
         type: string
 
@@ -116,6 +116,12 @@ jobs:
         run: |
           pip install -r scripts/gha/requirements.txt
 
+      - name: Pod repo add
+        shell: bash
+        # The pod install fails during the cmake build, so preinstall it.
+        run: |
+          pod repo add cocoapods https://github.com/CocoaPods/Specs.git
+
       - name: Install Unity
         uses: nick-invision/retry@v2
         with: