Run kernel demos and unit tests for PR changes (#645)

* Run kernel demos and unit tests for PR changes

Kernel demos check builds multiple demos from FreeRTOS/FreeRTOS and
unit tests check runs unit tests in FreeRTOS/FreeRTOS. Both of these
checks currently use main branch of FreeRTOS-Kernel. This commits
updates these checks to use the changes in the PR.

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

* Do not specify PR SHA explicitly as that is default

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

* Remove explicit PR SHA from kernel checks

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

---------

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>
diff --git a/.github/workflows/kernel-checks.yml b/.github/workflows/kernel-checks.yml
index b295033..a4627f0 100644
--- a/.github/workflows/kernel-checks.yml
+++ b/.github/workflows/kernel-checks.yml
@@ -28,7 +28,6 @@
       - name: Checkout Pull Request
         uses: actions/checkout@v2
         with:
-          ref:  ${{ github.event.pull_request.head.sha }}
           path: inspect
 
       # Collect all affected files
diff --git a/.github/workflows/kernel-demos.yml b/.github/workflows/kernel-demos.yml
index d6eace5..96a4c59 100644
--- a/.github/workflows/kernel-demos.yml
+++ b/.github/workflows/kernel-demos.yml
@@ -14,10 +14,11 @@
           submodules: 'recursive'
           fetch-depth: 1
 
-      - name: Fetch Kernel Submodule
-        shell: bash
-        run: |
-          git submodule update --checkout --init --depth 1 FreeRTOS/Source
+      # Checkout user pull request changes
+      - name: Checkout Pull Request
+        uses: actions/checkout@v2
+        with:
+          path: ./FreeRTOS/Source
 
       - name: Add msbuild to PATH
         uses: microsoft/setup-msbuild@v1.1
@@ -42,10 +43,11 @@
           submodules: 'recursive'
           fetch-depth: 1
 
-      - name: Fetch Kernel Submodule
-        shell: bash
-        run: |
-          git submodule update --checkout --init --depth 1 FreeRTOS/Source
+      # Checkout user pull request changes
+      - name: Checkout Pull Request
+        uses: actions/checkout@v2
+        with:
+          path: ./FreeRTOS/Source
 
       - name: Build WIN32-MingW Demo
         working-directory: FreeRTOS/Demo/WIN32-MingW
@@ -66,9 +68,11 @@
           submodules: 'recursive'
           fetch-depth: 1
 
-      - name: Fetch Kernel Submodule
-        shell: bash
-        run: git submodule update --checkout --init --depth 1 FreeRTOS/Source
+      # Checkout user pull request changes
+      - name: Checkout Pull Request
+        uses: actions/checkout@v2
+        with:
+          path: ./FreeRTOS/Source
 
       - name: Install GCC
         shell: bash
@@ -93,9 +97,11 @@
           submodules: 'recursive'
           fetch-depth: 1
 
-      - name: Fetch Kernel Submodule
-        shell: bash
-        run: git submodule update --checkout --init --depth 1 FreeRTOS/Source
+      # Checkout user pull request changes
+      - name: Checkout Pull Request
+        uses: actions/checkout@v2
+        with:
+          path: ./FreeRTOS/Source
 
       - name: Install MSP430 Toolchain
         shell: bash
@@ -120,9 +126,11 @@
           submodules: 'recursive'
           fetch-depth: 1
 
-      - name: Fetch Kernel Submodule
-        shell: bash
-        run: git submodule update --checkout --init --depth 1 FreeRTOS/Source
+      # Checkout user pull request changes
+      - name: Checkout Pull Request
+        uses: actions/checkout@v2
+        with:
+          path: ./FreeRTOS/Source
 
       - name: Install GNU ARM Toolchain
         shell: bash
diff --git a/.github/workflows/unit-tests.yml b/.github/workflows/unit-tests.yml
index a714b75..73e1808 100644
--- a/.github/workflows/unit-tests.yml
+++ b/.github/workflows/unit-tests.yml
@@ -12,7 +12,9 @@
         repository: FreeRTOS/FreeRTOS
         submodules: 'recursive'
         fetch-depth: 1
-    - name: Clone This Repo
+
+    # Checkout user pull request changes
+    - name: Checkout Pull Request
       uses: actions/checkout@v2
       with:
         path: ./FreeRTOS/Source