CI: Bump minimum macOS version to 13.0

Qt's minimum is 13, and I don't particularly feel like debugging issues
created if I work around it for an OS that hasn't been supported in over
a year.

.github/workflows/macos-build.yml

@@ -60,7 +60,7 @@ jobs:
       run: |
         mkdir build
         cd build
-        export MACOSX_DEPLOYMENT_TARGET=11.0
+        export MACOSX_DEPLOYMENT_TARGET=13.0
         cmake -DCMAKE_OSX_ARCHITECTURES="x86_64;arm64" -DCMAKE_BUILD_TYPE=Release -DENABLE_OPENGL=OFF -DCMAKE_PREFIX_PATH="$HOME/deps" -DCMAKE_INTERPROCEDURAL_OPTIMIZATION=ON -G Ninja ..
         cmake --build . --parallel
         mv bin/DuckStation.app .

README.md

@@ -114,7 +114,7 @@ You will need to re-add your game directories after switching to the AppImage.
 
 Universal macOS builds are provided for both x86_64 (Intel) and ARM64 (Apple Silicon).
 
-macOS Big Sur (11.0) is required, as this is also the minimum requirement for Qt.
+macOS Ventura (13.0) is required, as this is also the minimum requirement for Qt.
 
 To download:
  - Go to https://github.com/stenzek/duckstation/releases/tag/latest, and download `duckstation-mac-release.zip`.