ci: Fix the macOS and Windows builds

Both failures come from the runner images moving on, not from KDChart.

macos-latest no longer ships the AGL framework, which Qt links QtGui
against, so the shared build fails with "ld: framework 'AGL' not found"
(QTBUG-137687). Qt removed that linkage in 6.9.2, so use 6.9.3.

windows-latest is now Visual Studio 2025, whose STL dropped stdext,
which Qt 5.15.2 still uses in qvarlengtharray.h. That combination cannot
work and Qt 5.15.2 will not be fixed, so build Qt 5 on windows-2022 and
keep Qt 6 on windows-latest. The job count is unchanged.

Author: dfaure-kdab

.github/workflows/build.yml

@@ -23,6 +23,7 @@ jobs:
         os:
           - ubuntu-latest
           - windows-latest
+          - windows-2022
           - macos-latest
 
         build_type:
@@ -37,9 +38,21 @@ jobs:
           - qt_version: 5.15.2
             architectures: "x86_64"
 
-          - qt_version: 6.9.0
+          - qt_version: 6.9.3
             architectures: "x86_64;arm64"
 
+        exclude:
+          # Qt 5.15.2 uses stdext::checked_array_iterator, which Visual Studio
+          # 2025 removed, so it only builds on the older image
+          - os: windows-latest
+            config:
+              qt_version: 5.15.2
+              architectures: "x86_64"
+          - os: windows-2022
+            config:
+              qt_version: 6.9.3
+              architectures: "x86_64;arm64"
+
         include:
           - os: ubuntu-22.04
             build_type: Release