ci: explicit permissions

Author: FoxtrotSierra6829

.github/workflows/pr.yml

@@ -6,6 +6,8 @@ jobs:
     # Prevent running this on forks
     if: github.repository_owner == 'flybywiresim'
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
     steps:
       - name: Checkout source
         uses: actions/checkout@v2

.github/workflows/production.yml

@@ -9,6 +9,8 @@ jobs:
     # Prevent running this on forks
     if: github.repository_owner == 'flybywiresim'
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
     steps:
       - name: Checkout source
         uses: actions/checkout@v2

.github/workflows/staging.yml

@@ -9,6 +9,8 @@ jobs:
     # Prevent running this on forks
     if: github.repository_owner == 'flybywiresim'
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
     steps:
       - name: Checkout source
         uses: actions/checkout@v2