Fix build failing on MSRV

`tokio` pulled a dependency on a version of `socket2` that had a too
high MSRV. Because the `tokio` `socket2` version dependency range starts
at a too new `socket2` version, it's necessary to downgrade `tokio` to
the last version that has a MSRV compatible with ours.

.github/workflows/ogg.yml

@@ -19,6 +19,9 @@ jobs:
       with:
         toolchain: ${{ matrix.toolchain }}
         override: true
+    - name: Downgrade dependencies to comply with MSRV
+      if: matrix.toolchain == '1.56.1'
+      run: cargo update -p tokio --precise 1.29.1
     - name: Run no-default-features builds
       if: matrix.toolchain != '1.56.1'
       run: |