package/ci: once again switch to an an Xcode image that isn't removed.

Should have been done in d0e4e86df7, but
the deprecation notice wasn't clear about which versions are available,
at all.

package/ci/circleci.yml

@@ -20,22 +20,22 @@ executors:
   ubuntu-20_04:
     machine:
       image: ubuntu-2004:2024.11.1
-  # Images below 14.0.1 (and all x86 variants) are removed as of Nov 7, 2025
-  xcode-14_0:
+  # As of November 7, 2025, M4 is the default, and the oldest version there is
+  # 14.3.1.
+  xcode-14_3:
     macos:
-      xcode: 14.0.1
-    resource_class: macos.m1.medium.gen1
+      xcode: 14.3.1
   # Used by the static macOS build, to build against static MoltenVK. It
   # requires Xcode 14+ as 13 suffers from undefined _objc_msgSend$ symbols:
   #   https://stackoverflow.com/questions/73992337/flutter-build-is-ios-error-xcode-undefined-symbol-objc-msgsend
   # Then, linking to *.xcframework is only supported since CMake 3.28, before
   # that one has to pass the whole path to the *.a library:
   #   https://gitlab.kitware.com/cmake/cmake/-/issues/21752
-  # The Xcode 14.0.1 image has only CMake 3.26, 15.0.0 has 3.27.
-  xcode-15_1:
+  # The Xcode 14.0.1 image has only CMake 3.26, 15.0.0 has 3.27. As of November
+  # 7, 2025, M4 is the default, and the oldest version 15 there is 15.4.0.
+  xcode-15_4:
     macos:
-      xcode: 15.1.0
-    resource_class: macos.m1.medium.gen1
+      xcode: 15.4.0
   emscripten:
     docker:
     #  See Corrade's package/ci/circleci.yml
@@ -669,7 +669,7 @@ jobs:
         script: unix-desktop.sh
 
   macos-gl:
-    executor: xcode-14_0
+    executor: xcode-14_3
     environment:
       CMAKE_CXX_FLAGS: --coverage
       CONFIGURATION: Debug
@@ -685,7 +685,7 @@ jobs:
     - lcov
 
   macos-gles3:
-    executor: xcode-14_0
+    executor: xcode-14_3
     environment:
       CMAKE_CXX_FLAGS: --coverage
       CONFIGURATION: Debug
@@ -704,7 +704,7 @@ jobs:
     - lcov
 
   macos-vulkan:
-    executor: xcode-14_0
+    executor: xcode-14_3
     environment:
       CMAKE_CXX_FLAGS: --coverage
     steps:
@@ -720,7 +720,7 @@ jobs:
 
   macos-static:
     # Static MoltenVK needs newer Xcode and CMake
-    executor: xcode-15_1
+    executor: xcode-15_4
     environment:
       # STUPID yml interprets unquoted ON as a boolean
       BUILD_STATIC: "ON"
@@ -833,7 +833,7 @@ jobs:
         script: android-x86-vulkan.sh
 
   ios-gles3:
-    executor: xcode-14_0
+    executor: xcode-14_3
     environment:
       # STUPID yml interprets unquoted ON as a boolean
       TARGET_GLES2: "OFF"