ci: update mlx-swift submodule to latest main in integration tests

Both ci.yml and downstream_integration.yml check out SwiftLM with
submodules: recursive, which pins mlx-swift to SwiftLM's submodule
commit. When mlx-swift-lm PRs depend on new mlx-swift APIs (e.g.
preadIntoOffset from mlx-swift#10), the build fails because the
submodule pin is stale.

Fix: after replacing mlx-swift-lm with the PR checkout, also pull
mlx-swift to latest origin/main so new APIs are available.

Author: Aegis-AI

.github/workflows/ci.yml

@@ -123,6 +123,12 @@ jobs:
           # Replace the local submodule with the actively checked out code
           rm -rf mlx-swift-lm
           cp -r ../mlx-swift-lm .
+
+      - name: Update mlx-swift submodule to latest main
+        run: |
+          cd SwiftLM/mlx-swift
+          git fetch origin main
+          git checkout origin/main
           
       - name: Build SwiftLM
         run: |

.github/workflows/downstream_integration.yml

@@ -33,6 +33,14 @@ jobs:
           mkdir -p SwiftLM/mlx-swift-lm
           find . -mindepth 1 -maxdepth 1 ! -name "SwiftLM" -exec cp -r {} SwiftLM/mlx-swift-lm/ \;
 
+      - name: Update mlx-swift submodule to latest main
+        # SwiftLM's mlx-swift submodule pin may lag behind main.
+        # Pull latest so new APIs are available for the build.
+        run: |
+          cd SwiftLM/mlx-swift
+          git fetch origin main
+          git checkout origin/main
+
       - name: Install Metal Toolchain
         run: xcodebuild -downloadComponent MetalToolchain || true