chore: restrict GitHub workflow permissions - future-proof (#433)

Signed-off-by: Melissa Kilby <mkilby@apple.com>

Author: incertum

.github/workflows/62_snapshot_check.yml

@@ -1,5 +1,8 @@
 name: Smoke Test - 6.2 Nightly Swift Toolchain
 
+permissions:
+  contents: read
+
 on:
   schedule:
     - cron: '30 2 * * *'

.github/workflows/build_release.yml

@@ -1,5 +1,8 @@
 name: Build Release
 
+permissions:
+  contents: read
+
 on:
   workflow_dispatch:
     inputs:

.github/workflows/nightly_snapshot_check.yml

@@ -1,5 +1,8 @@
 name: Smoke Test - Nightly Swift Toolchain
 
+permissions:
+  contents: read
+
 on:
   schedule:
     - cron: '30 3 * * *'

.github/workflows/pull_request.yml

@@ -1,5 +1,8 @@
 name: Pull Request
 
+permissions:
+  contents: read
+
 on:
   pull_request:
     types: [opened, reopened, synchronize]