workflow: Add minimal Zephyr unit tests workflow for SOF CI

This commit introduces a basic GitHub Actions workflow to establish
the foundation for running SOF unit tests that have been ported from
cmocka to Zephyr ztest framework.

The workflow currently includes:
- Basic checkout step with proper fetch depth and tree filtering
- West initialization and workspace setup
- Environment verification step for debugging

This is the first iteration of the workflow, designed to validate
the basic environment setup before implementing the full test
execution pipeline. The workflow will be expanded in subsequent
commits to include:
- Zephyr SDK installation
- Complete environment configuration
- Unit test compilation and execution using west twister
- Test result collection and reporting

Testing approach:
- Triggers only on pull requests for safe testing
- Minimal resource usage during initial validation
- Debug output to verify workspace structure

The workflow follows SOF CI patterns and prepares the groundwork
for integrating ztest unit tests into the continuous integration
pipeline.

Signed-off-by: Tomasz Leman <tomasz.m.leman@intel.com>

Author: tmleman

.github/workflows/zephyr-unit-tests.yml

@@ -0,0 +1,56 @@
+---
+name: "Unit tests"
+on:
+  pull_request:
+    branches:
+      - 'main'
+
+permissions:
+  contents: read
+
+# Specifies group name that stops previous workflows if the name matches
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name }}-${{ github.head_ref || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  zephyr-utests:
+    name: Zephyr Unit Tests (ZTest)
+    runs-on: ubuntu-22.04
+    timeout-minutes: 10
+
+    steps:
+      - name: System dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install gcc-multilib g++-multilib
+
+      - name: Checkout SOF repository
+        uses: actions/checkout@v4
+        with:
+          path: ./workspace/sof
+          fetch-depth: 2
+          filter: 'tree:0'
+
+      - name: West update
+        run: |
+          cd workspace/sof
+          pip3 install west
+          west init -l
+          west update --narrow --fetch-opt=--filter=tree:0
+
+      - name: Install Python dependencies
+        run: |
+          cd workspace
+          pip3 install --user -r zephyr/scripts/requirements.txt
+
+      - name: Install Zephyr SDK
+        run: |
+          cd workspace/zephyr
+          west sdk install --version 0.16.9 -t x86_64-zephyr-elf
+
+      - name: Build and run unit tests
+        run: |
+          cd workspace
+          west twister --testsuite-root sof/test/ztest/unit/ --platform native_sim --verbose \
+           --inline-logs