CMake crashes while configuring (Incorrect use of CMake)

### Description



When I add a **Cpr** project to my project (according to the instructions in the **README.md**), the following code in the **Cpr** project's **CMakeLists.txt** causes **CMake** to crash during the configuration phase when using the **Ninja Multi-Config** generator on Linux (Ubuntu 20.04 / 22.04):



```cmake

get_property(isMultiConfig GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)

if (NOT isMultiConfig)

    set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS "${ALLOWED_BUILD_TYPES}")

    if (NOT CMAKE_BUILD_TYPE)

        set(CMAKE_BUILD_TYPE Debug CACHE STRING "" FORCE)

    elseif(NOT CMAKE_BUILD_TYPE IN_LIST ALLOWED_BUILD_TYPES)

        message(FATAL_ERROR "Invalid build type: ${CMAKE_BUILD_TYPE}")

    endif()

else()

    unset(CMAKE_BUILD_TYPE)

    foreach(TYPE ${ALLOWED_BUILD_TYPES})

        if (NOT ${TYPE} IN_LIST CMAKE_CONFIGURATION_TYPES)

            # !!! This command results in an error !!!

            list(APPEND CMAKE_CONFIGURATION_TYPES ${TYPE})

        endif()

    endforeach()

endif()

```



According to the discussion here https://gitlab.kitware.com/cmake/cmake/-/issues/24181, the cmake maintainer thinks that setting CMAKE_CONFIGURATION_TYPES in this manner should not happen. That is supposed to be a cache option for users to set.

Therefore, I ask you to remove the modification of the CMAKE_CONFIGURATION_TYPES variable inside the Cpr project.



### Example/How to Reproduce



The error is reproduced in the Ubuntu 20.04 / 22.04 operating system (most likely this error will also occur in other Linux distributions)



To reproduce, you need to create a project with the following **CMakeLists.txt** file:



```cmake

cmake_minimum_required(VERSION 3.20)

project(CMakeBugList)

include(FetchContent)

FetchContent_Declare(cpr GIT_REPOSITORY https://github.com/libcpr/cpr.git

                         GIT_TAG 871ed52d350214a034f6ef8a3b8f51c5ce1bd400) # The commit hash for 1.9.0. Replace with the latest from: https://github.com/libcpr/cpr/releases

FetchContent_MakeAvailable(cpr)

```



Now let's create a build directory and try to configure the project using the **Ninja Multi-Config** generator:



```shell

cmake ../Bug  -G "Ninja Multi-Config"

...

terminate called after throwing an instance of 'std::out_of_range'

  what():  map::at

Aborted (core dumped)

```



### Possible Fix



_No response_



### Where did you get it from?



GitHub (branch e.g. master), Other (specify in "Additional Context/Your Environment")



### Additional Context/Your Environment



- OS: Ubuntu 20.04 / 22.04

- Version: master / 1.9.2

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