AppVeyor: suppress debug messages about generate.stamp

(https://gitlab.kitware.com/cmake/cmake/issues/16783)

.appveyor.yml

@@ -38,7 +38,7 @@ install:
     7z x 3.3.3.zip -y > $null
     7z x 3.3.3.zip -y > $null
     $env:CMAKE_INCLUDE_PATH = "eigen-eigen-67e894c6cd8f"
     $env:CMAKE_INCLUDE_PATH = "eigen-eigen-67e894c6cd8f"
 build_script:
 build_script:
-- cmake -G "%CMAKE_GENERATOR%" -A "%CMAKE_ARCH%" -DPYBIND11_WERROR=ON
+- cmake -G "%CMAKE_GENERATOR%" -A "%CMAKE_ARCH%" -DPYBIND11_WERROR=ON -DCMAKE_SUPPRESS_REGENERATION=1
 - set MSBuildLogger="C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll"
 - set MSBuildLogger="C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll"
 - cmake --build . --config Release --target pytest -- /v:m /logger:%MSBuildLogger%
 - cmake --build . --config Release --target pytest -- /v:m /logger:%MSBuildLogger%
 - cmake --build . --config Release --target test_cmake_build -- /v:m /logger:%MSBuildLogger%
 - cmake --build . --config Release --target test_cmake_build -- /v:m /logger:%MSBuildLogger%