Add empty permissions block in Github Actions configs (#3694)

To restrict all permissions by default (CodeQL warning)

(cherry picked from commit 4356b43)

Author: roji

.github/workflows/build.yml

@@ -10,6 +10,9 @@ on:
       - v*
   pull_request:
 
+permissions:
+  contents: read
+
 env:
   postgis_version: 3
   DOTNET_SKIP_FIRST_TIME_EXPERIENCE: true

.github/workflows/trigger-doc-build.yml

@@ -8,6 +8,9 @@ on:
     branches:
       - docs
 
+permissions:
+  contents: read
+
 jobs:
   build:
     runs-on: ubuntu-22.04