Increasing Minimum Required CMake version to 3.26

[jkoritzinsky]

We are increasing the minimum required version of CMake in the dotnet/runtime repo (and as a result dotnet/dotnet as well) to CMake 3.26 with #120823.

The newest LTS/major version of all commonly used Linux distros include at least CMake 3.26, and Visual Studio 2022 and newer bundle CMake 3.31 or newer, so this change may not require any adjustments locally.

If you are running an older version of CMake, you may need to install a newer version.

For Windows and Mac, newer versions can be found at Download CMake

For Ubuntu 22.04 users, Kitware APT Repository provides newer versions, as does Snap.

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