Pin petgraph

Author: G8XSU

.github/workflows/build.yml

@@ -43,6 +43,7 @@ jobs:
         if: matrix.msrv
         run: |
           cargo update -p hashlink --precise "0.8.2" --verbose # hashlink 0.8.3 requires hashbrown 0.14, requiring 1.64.0
+          cargo update -p petgraph --precise "0.6.3" --verbose # petgraph v0.6.4, requires rustc 1.64 or newer
       - name: Build on Rust ${{ matrix.toolchain }}
         run: cargo build --verbose --color always
       - name: Build with UniFFI support on Rust ${{ matrix.toolchain }}