ci: Use -Zmiri-many-seeds on schedule job

.github/workflows/ci.yml

@@ -704,14 +704,16 @@ jobs:
           - target: powerpc64le-unknown-linux-gnu
           - target: s390x-unknown-linux-gnu
     runs-on: ubuntu-latest
-    timeout-minutes: 60
+    timeout-minutes: 180
     steps:
       - uses: taiki-e/checkout-action@v1
       - uses: taiki-e/github-actions/install-rust@nightly
       - uses: taiki-e/install-action@cargo-hack
       # - run: sudo apt-get -o Acquire::Retries=10 -qq update && sudo apt-get -o Acquire::Retries=10 -o Dpkg::Use-Pty=0 install -y --no-install-recommends moreutils
       - run: printf '%s\n' "TARGET=--target=${{ matrix.target }}" >>"${GITHUB_ENV}"
         if: matrix.target != 'x86_64-unknown-linux-gnu'
+      - run: printf '%s\n' "MIRIFLAGS=-Zmiri-many-seeds=0..8" >>"${GITHUB_ENV}"
+        if: github.event_name == 'schedule' && matrix.target == 'x86_64-unknown-linux-gnu'
       - run: tools/test.sh miri ${TARGET:-}
         env:
           RUSTDOCFLAGS: ${{ env.RUSTDOCFLAGS }} ${{ matrix.flags }}