FetchContent_Populate failed to get HEAD

FetchContent_Populate only pulls from HEAD & won't update when the head moves.

Performing update step for 'imstkexternalprojecttemplate-populate'
1>  CMake Error at C:/Repos/iMSTK/buildMsvc17/Innerbuild/Testing/imstkexternalprojecttemplate-subbuild/imstkexternalprojecttemplate-populate-prefix/tmp/imstkexternalprojecttemplate-populate-gitupdate.cmake:25 (message):
1>    Failed to get the hash for HEAD:
1>
1>    fatal: unsafe repository
1>    ('C:/Repos/iMSTK/buildMsvc17/Innerbuild/Testing/iMSTKExternalProjectTemplate'
1>    is owned by someone else)
1>
1>    To add an exception for this directory, call:
1>
1>
1>
1>    	git config --global --add safe.directory
1>    C:/Repos/iMSTK/buildMsvc17/Innerbuild/Testing/iMSTKExternalProjectTemplate

Nothing in the repository changed but iMSTKExternalProjectTemplate was updated.