fix: decrease max-parallel from 10 to 5 for provider upgrades (#228)

We continue to run into Github errors with our user creating PRs and
setting labels. Hopefully this change improves that situation and fails
less.

Ideally, the Github CLI would honor rate limits and retry automatically,
but it doesn't support that at this time:
cli/cli#3292

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.github/workflows/upgrade-repositories.yml

@@ -26,7 +26,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix: ${{fromJSON(needs.build-provider-matrix.outputs.matrix)}}
-      max-parallel: 10
+      max-parallel: 5
     steps:
       - name: Checkout this repository
         uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3