ci: add top-level permissions to workflow files

Add `permissions: contents: read` at the workflow level for
bump-libs.yaml, format.yaml, master.yaml, and release.yaml to follow
the principle of least privilege. Job-level permissions that require
elevated access will override this as expected.

Signed-off-by: Gagan H R <hrgagan4@gmail.com>

.github/workflows/bump-libs.yaml

@@ -6,6 +6,9 @@ on:
   schedule:
     - cron: '30 6 * * 1' # on each monday 6:30
 
+permissions:
+  contents: read
+
 # Checks if any concurrent jobs is running for kernels CI and eventually cancel it.
 concurrency:
   group: bump-libs-ci

.github/workflows/format.yaml

@@ -6,6 +6,9 @@ on:
       - master
       - "release/**"
 
+permissions:
+  contents: read
+
 jobs:
   format:
     name: format code 🐲

.github/workflows/master.yaml

@@ -3,6 +3,9 @@ on:
   push:
     branches: [master]
 
+permissions:
+  contents: read
+
 # Checks if any concurrent jobs is running for master CI and eventually cancel it
 concurrency:
   group: ci-master

.github/workflows/release.yaml

@@ -3,6 +3,9 @@ on:
   release:
     types: [published]
 
+permissions:
+  contents: read
+
 # Checks if any concurrent jobs is running for release CI and eventually cancel it.
 concurrency:
   group: ci-release