ser minimal permissions to linux.yml

Signed-off-by: Joyce <joycebrum@google.com>
diff --git a/.github/workflows/linux.yml b/.github/workflows/linux.yml
index 2a6ed94..0160c3b 100644
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@@ -19,6 +19,9 @@
     pull_request:
         branches:
             - main
+            
+permissions:
+    contents: read
 
 jobs:
   ubuntu-cmake-install: