Work around an issue with github builders

.github/workflows/main.yml

@@ -264,7 +264,7 @@ jobs:
         CFLAGS: /Zi
         CXXFLAGS: /Zi
         LDFLAGS: /DEBUG:FULL /OPT:REF /OPT:ICF
-      run: cmake -Bbuild -Smegasource -T v143 -A ${{ matrix.platform }} --install-prefix %CD%\install -DCMAKE_PDB_OUTPUT_DIRECTORY=%CD%\pdb ${{ steps.vars.outputs.moredef }}
+      run: cmake -Bbuild -Smegasource -T v143 -A ${{ matrix.platform }} --install-prefix %CD%\install -DCMAKE_PDB_OUTPUT_DIRECTORY=%CD%\pdb -DCMAKE_SYSTEM_VERSION=10.0.26100.0 ${{ steps.vars.outputs.moredef }}
     - name: Install
       run: cmake --build build --target PACKAGE --config Release -j2
     - name: Copy LuaJIT lua51.pdb