CI: disable RISC-V runners for now

these are taking too long. let's use a different workflow for now until
these runs are not holding up the pipeline, then they can be
reintroduced on master branch

.github/workflows/ci.yaml

@@ -50,24 +50,6 @@ jobs:
         uses: actions/checkout@v4
       - name: Build and Test
         run: sh ci/aarch64-linux-release.sh
-  riscv64-linux-debug:
-    if: ${{ github.event_name == 'push' }}
-    timeout-minutes: 1020
-    runs-on: [self-hosted, Linux, riscv64]
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-      - name: Build and Test
-        run: sh ci/riscv64-linux-debug.sh
-  riscv64-linux-release:
-    if: ${{ github.event_name == 'push' }}
-    timeout-minutes: 900
-    runs-on: [self-hosted, Linux, riscv64]
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-      - name: Build and Test
-        run: sh ci/riscv64-linux-release.sh
   x86_64-macos-release:
     runs-on: "macos-13"
     env: