ci: add minimal permissions to workflows

.github/workflows/audit.yml

@@ -5,6 +5,10 @@ name: Security audit
 on:
   schedule:
     - cron: "0 0 * * *"
+
+permissions:
+  contents: read
+
 jobs:
   audit:
     runs-on: ubuntu-latest

.github/workflows/documentation.yml

@@ -17,6 +17,9 @@ on:
       - 'src/uu/*/locales/en-US.ftl'
       - 'Cargo.toml'
 
+permissions:
+  contents: read
+
 jobs:
   check-doc:
     name: Verify uudoc generates correct documentation

.github/workflows/manpage-lint.yml

@@ -22,6 +22,9 @@ on:
       - 'GNUmakefile'
       - '.github/workflows/manpage-lint.yml'
 
+permissions:
+  contents: read
+
 jobs:
   manpage-lint:
     name: Validate manpages with mandoc