Use personal access token

Turns out you can't modify org members using a Github action's GITHUB_TOKEN even
if you have it set to `write-all`. You've got to use a personal access token.
I'm using mine for now. If I'm ever removed from the org, the GH membership
management will start failing through Pulumi.

.github/workflows/preview.yml

@@ -30,7 +30,7 @@ jobs:
           stack-name: slatedb/slatedb-pulumi/prod
           comment-on-pr: true
         env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.GH_PERSONAL_ACCESS_TOKEN }}
           DISCORD_TOKEN: ${{ secrets.DISCORD_TOKEN }}
           CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }}
           PULUMI_ACCESS_TOKEN: ${{ secrets.PULUMI_ACCESS_TOKEN }}

.github/workflows/up.yml

@@ -25,7 +25,7 @@ jobs:
           command: up
           stack-name: slatedb/slatedb-pulumi/prod
         env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.GH_PERSONAL_ACCESS_TOKEN }}
           DISCORD_TOKEN: ${{ secrets.DISCORD_TOKEN }}
           CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }}
           PULUMI_ACCESS_TOKEN: ${{ secrets.PULUMI_ACCESS_TOKEN }}