update-via-pacman: install the correct git-extra package at the end

The script still had one left-over from the MINGW64 flavor of Git
for Windows' SDK: the final `pacman` call that ensures that the
`git-extra` package is installed (mostly for the benefit of letting
its post-install script modify all the things in a regular MSYS2
setup to what Git for Windows needs and which cannot be configured
in any other way).

With this commit, this script now installs the UCRT64 flavor of
that package, and the migration of this script is now complete.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

update-via-pacman.ps1

@@ -148,4 +148,4 @@ if (!(Test-Path cmd\git.exe -PathType Leaf)) {
 }
 
 # Wrapping up: re-install mingw-w64-git-extra
-bash -lc "pacman -S --overwrite=\* --noconfirm mingw-w64-x86_64-git-extra"
+bash -lc "pacman -S --overwrite=\* --noconfirm mingw-w64-ucrt-x86_64-git-extra"