Add ShellCheck GitHub Actions workflow

Add a shellcheck workflow that validates all .sh scripts on PRs.
Runs at severity=error to catch real bugs without blocking on
style warnings.

Fix two existing shellcheck errors (SC2145) in test scripts where
"$@" was used in echo strings instead of "$*".

Author: sebrandon1

.github/workflows/shellcheck.yml

@@ -0,0 +1,28 @@
+---
+name: ShellCheck
+
+on:
+  pull_request:
+    branches:
+      - main
+    paths:
+      - "**/*.sh"
+
+permissions:
+  contents: read
+
+jobs:
+  shellcheck:
+    name: Validate Shell Scripts
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run ShellCheck
+        run: |
+          find . -name '*.sh' \
+            -not -path './.git/*' \
+            -not -path './venv/*' \
+            -not -path './.venv/*' \
+            -print0 | xargs -0 shellcheck --severity=error

telco-ran/configuration/extra-manifests-builder/01-container-mount-ns-and-kubelet-conf/test.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 fatal() {
-    echo "FATAL: $@"
+    echo "FATAL: $*"
     exit 1
 }
 

telco-ran/configuration/extra-manifests-builder/08-set-rcu-normal/test.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 fatal() {
-  echo "FATAL: $@"
+  echo "FATAL: $*"
   exit 1
 }