[TASK] Narrow the permissions for the CI workflows (#1632)

https://docs.zizmor.sh/audits/#excessive-permissions

Part of #1628

Author: oliverklee

.github/workflows/ci.yml

@@ -10,6 +10,9 @@ on:
 
 name: CI
 
+permissions:
+    contents: read
+
 jobs:
     php-lint:
         name: PHP Lint

.github/workflows/codecoverage.yml

@@ -8,6 +8,9 @@ on:
 
 name: Code coverage
 
+permissions:
+    contents: read
+
 jobs:
     code-coverage:
         name: Code coverage