ci: bump microsoft/setup-msbuild from v1 to v2

ci: bump microsoft/setup-msbuild from v1 to v2

The main benefit: The new version uses a node.js version that is not yet
deprecated.

Links:
- [Release notes](https://github.com/microsoft/setup-msbuild/releases)
- [Changelog](https://github.com/microsoft/setup-msbuild/blob/main/building-release.md)
- [Commits](https://github.com/microsoft/setup-msbuild/compare/v1...v2)

This patch was originally by GitHub's Dependabot, but I cannot attribute
that bot properly because it has no dedicated email address. Probably
because it hasn't reached legal age yet, or something.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>