Add Gtk3Backend to macOS and Linux CI, fix Windows CI

Author: stackotter

.github/workflows/swift-linux.yml

@@ -17,13 +17,14 @@ jobs:
     - name: Install Dependencies
       run: |
         sudo apt update && \
-        sudo apt install -y libgtk-4-dev clang
+        sudo apt install -y libgtk-4-dev libgtk-3-dev clang
     - name: Build
       run: |
-        swift build --target GtkCodeGen && \
         cd Examples && \
+        swift build --target GtkCodeGen && \
         swift build --target SwiftCrossUI && \
         swift build --target GtkBackend && \
+        swift build --target Gtk3Backend && \
         swift build --target CounterExample && \
         swift build --target ControlsExample && \
         swift build --target RandomNumberGeneratorExample && \

.github/workflows/swift-macos.yml

@@ -16,13 +16,14 @@ jobs:
       run: sudo xcode-select -switch /Applications/Xcode_15.4.app
     - uses: actions/checkout@v3
     - name: Install Dependencies
-      run: brew install pkg-config gtk4 || echo "This step 'fails' every time but it's just a brew linking error - not important."
+      run: brew install pkg-config gtk4 gtk+3 || echo "This step 'fails' every time but it's just a brew linking error - not important."
     - name: Build
       run: |
-        swift build --target GtkCodeGen && \
         cd Examples && \
+        swift build --target GtkCodeGen && \
         swift build --target SwiftCrossUI && \
         swift build --target GtkBackend && \
+        swift build --target Gtk3Backend && \
         swift build --target AppKitBackend && \
         swift build --target CounterExample && \
         swift build --target ControlsExample && \

.github/workflows/swift-windows.yml

@@ -24,8 +24,8 @@ jobs:
     - name: Setup
       uses: compnerd/[email protected]
       with:
-        branch: swift-6.0-release
-        tag: 6.0-RELEASE
+        branch: swift-5.10-release
+        tag: 5.10-RELEASE
 
     - name: Compute vcpkg Triplet
       id: triplet
@@ -60,6 +60,6 @@ jobs:
         PKG_CONFIG_PATH: ${{ github.workspace }}/vcpkg_installed/${{ steps.triplet.outputs.lowercase }}/lib/pkgconfig
       # Only build the library target to work around apple/swift-package-manager#6644
       run: swift build --target SwiftCrossUI -v
-
-    - name: Build WinUIBackend
-      run: swift build --target WinUIBackend
+    # Requires 6.0, and 6.0 is broken in CI for now.
+    # - name: Build WinUIBackend
+    #   run: swift build --target WinUIBackend