Fix latest deps (#13743)

.github/workflows/latest_deps.yml

@@ -84,6 +84,12 @@ jobs:
         if: ${{ matrix.postgres-version }}
         timeout-minutes: 2
         run: until pg_isready -h localhost; do sleep 1; done
+
+      # We nuke the local copy, as we've installed synapse into the virtualenv
+      # (rather than use an editable install, which we no longer support). If we
+      # don't do this then python can't find the native lib.
+      - run: rm -rf synapse/
+
       - run: python -m twisted.trial --jobs=2 tests
         env:
           SYNAPSE_POSTGRES: ${{ matrix.database == 'postgres' || '' }}
@@ -128,6 +134,14 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
+
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: stable
+            override: true
+      - uses: Swatinem/rust-cache@v2
+
       - name: Ensure sytest runs `pip install`
         # Delete the lockfile so sytest will `pip install` rather than `poetry install`
         run: rm /src/poetry.lock

changelog.d/13743.misc

@@ -0,0 +1 @@
+Add a stub Rust crate.