Re-enable Complement Crypto tests (#5257)

Since matrix-org/complement-crypto#235 these
should be more reliable.

This reverts commit 4d59291.

Author: andybalaam

.github/workflows/tests.yml

@@ -88,7 +88,7 @@ jobs:
 
     complement-crypto:
         name: "Run Complement Crypto tests"
-        if: false # disabled due to flakiness
+        if: github.event_name == 'merge_group'
         permissions: read-all # zizmor: ignore[excessive-permissions]
         uses: matrix-org/complement-crypto/.github/workflows/single_sdk_tests.yml@main # zizmor: ignore[unpinned-uses]
         with: