Test both dunfell and hardknott

.github/workflows/main.yml

@@ -1,9 +1,14 @@
 on: [pull_request]
 jobs:
   build:
-    env:
-      YOCTO_VERSION: 3.3.2
-      YOCTO_BRANCH: hardknott
+    strategy:
+      matrix:
+        yoctobranch: [dunfell, hardknott]
+        include:
+          - yoctobranch: hardknott
+            yoctoversion: 3.3.2
+          - yoctobranch: dunfell
+            yoctoversion: 3.1.9
     runs-on: self-hosted
     steps:
       - uses: actions/checkout@v2
@@ -11,20 +16,18 @@ jobs:
           path: 'meta-rust'
       - name: Fetch poky
         run: |
-          mv poky/build/sstate-cache . || true
           rm -rf poky meta-openembedded
-          git clone -b $YOCTO_BRANCH --single-branch git://git.yoctoproject.org/poky
-          git clone -b $YOCTO_BRANCH --single-branch git://git.openembedded.org/meta-openembedded
+          git clone -b ${{ matrix.yoctobranch }} --single-branch git://git.yoctoproject.org/poky
+          git clone -b ${{ matrix.yoctobranch }} --single-branch git://git.openembedded.org/meta-openembedded
       - name: Configure build
         run: |
           cd poky
           . oe-init-build-env
-          mv ../../sstate-cache . || true
           bitbake-layers add-layer ../../meta-openembedded/meta-oe
           bitbake-layers add-layer ../../meta-rust
           echo 'PARALLEL_MAKE:pn-rust-llvm-native = "-j2"' >> conf/local.conf
           echo 'TOOLCHAIN_HOST_TASK:append = " packagegroup-rust-cross-canadian-${MACHINE}"' >> conf/local.conf
-          echo "SSTATE_MIRRORS = \"file://.* http://sstate.yoctoproject.org/$YOCTO_VERSION/PATH;downloadfilename=PATH \\n\"" >> conf/local.conf
+          echo "SSTATE_MIRRORS = \"file://.* http://sstate.yoctoproject.org/${{ matrix.yoctoversion }}/PATH;downloadfilename=PATH \\n\"" >> conf/local.conf
           echo 'PREFERRED_PROVIDER_virtual/kernel = "linux-dummy"' >> conf/local.conf
       - name: Run bitbake
         run: |