chore(ci): upgrade QEMU to 6.1.0

Fixes test failures on `qemu_sifive_u_s_rv{32,64}`.

Author: yvt

.github/actions/install-qemu/action.yml

@@ -4,7 +4,7 @@ inputs:
   version:
     description: QEMU version to install
     required: true
-    default: 5.1.0
+    default: 6.1.0
   target-list:
     description: List of targets to build
     required: true

.github/workflows/ci.yml

@@ -235,15 +235,15 @@ jobs:
       - name: Install dependencies (Linux)
         run: |
           sudo apt-get update
-          sudo apt-get install libusb-1.0-0-dev libudev-dev
+          sudo apt-get install libusb-1.0-0-dev libudev-dev ninja-build
 
       - name: Cache QEMU's built binaries
         uses: actions/cache@v2
         with:
           path: ~/.qemu
           key: ${{ runner.os }}-ci-qemu-arm_riscv
 
-      - name: Install QEMU 5.1.0 from source
+      - name: Install QEMU 6.1.0 from source
         uses: ./.github/actions/install-qemu
         with:
           target-list: arm-softmmu,riscv32-softmmu,riscv64-softmmu