ci: restrict permissions of GITHUB_TOKEN

closes #1616

.github/workflows/build.yml

@@ -1,5 +1,8 @@
 name: build
 
+permissions:
+  contents: write
+
 on:
   pull_request:
     branches: [ master ]

.github/workflows/publish.yml

@@ -3,6 +3,9 @@
 
 name: publish to pypi
 
+permissions:
+  contents: write
+
 on:
   release:
     types: [published]