GitHub Actions: Update to checkout action v2.3.1 with fetch-depth: 0

Checkout v2+ checks out a local branch rather than a detached head.
Branch name for releases should now be master instead of HEAD.

.github/workflows/rolling-release.yml

@@ -10,8 +10,9 @@ jobs:
   windows-build:
     runs-on: windows-2019
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2.3.1
       with:
+        fetch-depth: 0
         submodules: true
 
     - name: Compile release build
@@ -56,7 +57,9 @@ jobs:
   linux-build:
     runs-on: ubuntu-20.04
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2.3.1
+      with:
+        fetch-depth: 0
 
     - name: Install packages
       shell: bash