Revert "Pin rust for coverage ci to nightly-2022-06-30 to circumvent rust-lang/rust#98833"

This reverts commit 3356288.

Author: kezhuw

.github/workflows/ci.yml

@@ -58,7 +58,7 @@ jobs:
     - name: Install latest nightly
       uses: actions-rs/toolchain@v1
       with:
-          toolchain: nightly-2022-06-30
+          toolchain: nightly
           override: true
           components: llvm-tools-preview
     - run: cargo install grcov