allow using aosp sign key (#113)

.github/workflows/build.yml

@@ -112,8 +112,8 @@ jobs:
             echo "$BOOT_SIGN_KEY" > ./kernel-build-tools/linux-x86/share/avb/testkey_rsa2048.pem
             echo "BOOT_SIGN_KEY_PATH=$GITHUB_WORKSPACE/kernel-build-tools/linux-x86/share/avb/testkey_rsa2048.pem" >> $GITHUB_ENV
           else
-            echo "BOOT_SIGN_KEY is not set. Exiting..."
-            exit 1
+            echo "BOOT_SIGN_KEY is not set. Using AOSP sign key..."
+            echo "BOOT_SIGN_KEY_PATH=$GITHUB_WORKSPACE/kernel-build-tools/linux-x86/share/avb/testkey_rsa2048.pem" >> $GITHUB_ENV
           fi
 
       - name: Install Repo