ci: Disable RISC-V workflows temporarily

The workflows are very flaky and have been failing the majority of the
time recently.

Fixes: #7758

Signed-off-by: Rob Bradford <rbradford@meta.com>

.github/workflows/preview-riscv64-build.yaml

@@ -1,30 +0,0 @@
-name: Cloud Hypervisor RISC-V 64-bit kvm build Preview
-on: [pull_request, merge_group]
-concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}-${{ github.event_name }}
-  cancel-in-progress: true
-
-jobs:
-  build:
-    name: Cargo
-    runs-on: riscv64-qemu-host
-    strategy:
-      fail-fast: false
-
-    steps:
-      - name: Code checkout
-        uses: actions/checkout@v6
-        with:
-          fetch-depth: 0
-
-      - name: Install Rust toolchain
-        run: /opt/scripts/exec-in-qemu.sh rustup default 1.89.0
-
-      - name: Build test (kvm)
-        run: /opt/scripts/exec-in-qemu.sh cargo build --locked --no-default-features --features "kvm" -p cloud-hypervisor
-
-      - name: Clippy test (kvm)
-        run: /opt/scripts/exec-in-qemu.sh cargo clippy --locked --no-default-features --features "kvm" -p cloud-hypervisor
-
-      - name: Check no files were modified
-        run: test -z "$(git status --porcelain)"

.github/workflows/preview-riscv64-modules.yaml

@@ -1,39 +0,0 @@
-name: Cloud Hypervisor RISC-V 64-bit Preview
-on: [pull_request, merge_group]
-concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}-${{ github.event_name }}
-  cancel-in-progress: true
-
-jobs:
-  build:
-    name: Cargo
-    runs-on: riscv64-qemu-host
-    strategy:
-      fail-fast: false
-      matrix:
-        module:
-          - hypervisor
-          - arch
-          - vm-allocator
-          - devices
-
-    steps:
-      - name: Code checkout
-        uses: actions/checkout@v6
-        with:
-          fetch-depth: 0
-
-      - name: Install Rust toolchain
-        run: /opt/scripts/exec-in-qemu.sh rustup default 1.89.0
-
-      - name: Build ${{ matrix.module }} Module (kvm)
-        run: /opt/scripts/exec-in-qemu.sh cargo build --locked -p ${{ matrix.module }} --no-default-features --features "kvm"
-
-      - name: Clippy ${{ matrix.module }} Module (kvm)
-        run: /opt/scripts/exec-in-qemu.sh cargo clippy --locked -p ${{ matrix.module }} --no-default-features --features "kvm" -- -D warnings
-
-      - name: Test ${{ matrix.module }} Module (kvm)
-        run: /opt/scripts/exec-in-qemu.sh cargo test --locked -p ${{ matrix.module }} --no-default-features --features "kvm"
-
-      - name: Check no files were modified
-        run: test -z "$(git status --porcelain)"