ci: declare workflow-level contents: read on 4 workflows

Pins the default GITHUB_TOKEN to contents: read on the workflows in
.github/workflows/ that don't call a GitHub API beyond the initial
checkout. The other workflows in this directory are left implicit
because they need write scopes that a maintainer is better placed
to declare.

Motivation: CVE-2025-30066 (March 2025 tj-actions/changed-files
compromise) exfiltrated GITHUB_TOKEN from workflow logs. Per-workflow
caps bound runtime authority irrespective of repo or org default,
give drift protection if the default ever widens, and are credited
per-file by the OpenSSF Scorecard Token-Permissions check.

YAML validated locally with yaml.safe_load.

Signed-off-by: Arpit Jain <arpitjain099@gmail.com>

Author: arpitjain099

.github/workflows/license-header-check.yml

@@ -19,6 +19,9 @@ on:
   pull_request:
     types: [opened, synchronize, reopened]
 
+permissions:
+  contents: read
+
 jobs:
   license-header-check:
     runs-on: ubuntu-latest

.github/workflows/markdown-links-check.yml

@@ -19,6 +19,9 @@ on:
   pull_request:
     types: [opened, synchronize, reopened]
 
+permissions:
+  contents: read
+
 jobs:
   markdown-link-check:
     runs-on: ubuntu-latest

.github/workflows/mvn-verify-check.yml

@@ -35,6 +35,9 @@ env:
     -Daether.connector.http.connectionMaxTtl=30
     -Drapids.secondaryCacheDir=$HOME/.m2/repository/.sbt/1.0/zinc/org.scala-sbt
 
+permissions:
+  contents: read
+
 jobs:
   cache-dependencies:
     runs-on: ubuntu-latest

.github/workflows/shell-check.yml

@@ -19,6 +19,9 @@ on:
   pull_request:
     types: [opened, synchronize, reopened]
 
+permissions:
+  contents: read
+
 jobs:
   shell-check:
     runs-on: ubuntu-latest