ci: add minimum GitHub token permissions for workflows

Signed-off-by: Ashish Kurmi <akurmi@stepsecurity.io>

.github/workflows/release.yml

@@ -5,6 +5,9 @@ on:
   release:
     types: [published]
 
+permissions:
+  contents: read
+
 jobs:
   generate:
     name: 'Update node-red-docker image'

.github/workflows/tests.yml

@@ -6,8 +6,14 @@ on:
   pull_request:
     branches: [ master, dev ]
 
+permissions:
+  contents: read
+
 jobs:
   build:
+    permissions:
+      checks: write  # for coverallsapp/github-action to create new checks
+      contents: read  # for actions/checkout to fetch code
     runs-on: ubuntu-latest
     strategy:
       matrix: