one unity version at a time

Author: StephenHodgson

.github/workflows/validate.yml

@@ -35,6 +35,7 @@ jobs:
     strategy:
       matrix: ${{ fromJSON(needs.setup.outputs.jobs) }}
       fail-fast: false
+      max-parallel: 1
     secrets: inherit
     uses: ./.github/workflows/build.yml
     with: