ci: declare contents: read on validate_pyinstaller workflow (aws#8992)

PR-triggered build of the PyInstaller bundle for linux/macos/windows.
Each job is a build matrix that runs docker + python + pyinstaller. No
push, no comment, no release write - contents: read suffices.

Signed-off-by: Arpit Jain <arpitjain099@gmail.com>
Co-authored-by: Reed Hamilton <reedham@amazon.com>

Author: arpitjain099

.github/workflows/validate_pyinstaller.yml

@@ -8,6 +8,9 @@ on:
 env:
   CI_OVERRIDE: "1"
 
+permissions:
+  contents: read
+
 jobs:
   build-for-linux:
     name: build-pyinstaller-linux