See #26 as well.

If you accidentally provide an invalid arch (like Win32 instead of x86), this action will report success, but will not properly configure the PATH.

For example:

Run ilammy/msvc-dev-cmd@v1.5.0
  with:
    arch: Win32
Found with vswhere: C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvarsall.bat
Configured Developer Command Prompt

Running CMake after this then tries to use GCC.