Work around upstream minimal versions issue

Author: djc

.github/workflows/CI.yml

@@ -97,6 +97,7 @@ jobs:
     - name: install Rust nightly
       uses: dtolnay/rust-toolchain@nightly
     - uses: dtolnay/rust-toolchain@stable
+    - run: cargo update -p thiserror@1 --precise 1.0.31 # https://github.com/open-telemetry/opentelemetry-rust/pull/2406
     - name: install cargo-hack
       uses: taiki-e/install-action@cargo-hack
     - name: install cargo-minimal-versions