ci: scope down GitHub Token permissions (#1112)

* ci: scope down permissions for pypi-release.yaml
* ci: scope down permissions for schema-updater.yaml
* ci: scope down permissions for pr-ci.yaml

Author: AdnaneKhan

.github/workflows/pr-ci.yaml

@@ -4,6 +4,9 @@ name: CloudFormation CLI Pull Request CI
 
 on: [push, pull_request]
 
+permissions:
+  contents: read
+
 jobs:
   build:
     env:

.github/workflows/pypi-release.yaml

@@ -5,6 +5,9 @@ on:
   release:
     types: [ published ]
 
+permissions:
+  contents: read
+
 jobs:
   build:
     runs-on: ubuntu-latest

.github/workflows/schema-updater.yaml

@@ -2,6 +2,10 @@ on:
   schedule:
     - cron: '0 0 * * *'
   workflow_dispatch: # Enables on-demand/manual triggering: https://docs.github.com/en/free-pro-team@latest/actions/managing-workflow-runs/manually-running-a-workflow
+permissions:
+  contents: write
+  pull-requests: write
+
 jobs:
   schema-updater:
     runs-on: ubuntu-latest