Set least-privilege workflow permissions

Author: ripred

.github/workflows/arduino-lint.yml

@@ -2,6 +2,9 @@
 name: Arduino-lint
 
 on: [push, pull_request]
+permissions:
+  contents: read
+
 jobs:
   lint:
     runs-on: ubuntu-latest

.github/workflows/arduino_test_runner.yml

@@ -3,6 +3,9 @@ name: Arduino CI
 
 on: [push, pull_request]
 
+permissions:
+  contents: read
+
 jobs:
   runTest:
     runs-on: ubuntu-latest

.github/workflows/jsoncheck.yml

@@ -6,6 +6,9 @@ on:
       - '**.json'
   pull_request:
 
+permissions:
+  contents: read
+
 jobs:
   test:
     runs-on: ubuntu-latest