[chore]: add permissions to github workflows per recommendation (#369)

might resolve:
https://github.com/square/workflow-swift/security/code-scanning/12

Author: jamieQ

.github/workflows/docs.yaml

@@ -1,5 +1,9 @@
 name: Generate and publish docs
 
+permissions:
+  contents: read
+  pull-requests: write
+
 on:
   push:
     branches: [ main ]

.github/workflows/swift.yaml

@@ -1,5 +1,9 @@
 name: Swift CI
 
+permissions:
+  contents: read
+  pull-requests: write
+
 on:
   push:
     branches: