Fix complement tests using the wrong path (#12933)

.github/workflows/tests.yml

@@ -372,7 +372,7 @@ jobs:
       # Attempt to check out the same branch of Complement as the PR. If it
       # doesn't exist, fallback to HEAD.
       - name: Checkout complement
-        run: .ci/scripts/checkout_complement.sh
+        run: synapse/.ci/scripts/checkout_complement.sh
 
       - run: |
           set -o pipefail

changelog.d/12933.misc

@@ -0,0 +1 @@
+Test Synapse against Complement with workers.