Try again launching Android Studio from a CMD where you have set a simplified PATH, putting your Git for Windows installation first.
See this answer as an example:
set PATH=C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\
set GH=C:\path\to\git
set PATH=%GH%\bin;%GH%\usr\bin;%GH%\mingw64\bin;%PATH%
set PATH=%PATH%;/path/to/Android Studio/bin
Make sure you have uncompressed the latest Git For Windows (like PortableGit-2.15.0-64-bit.7z.exe
) anywhere you want.