.github: enable windows builds on microsoft fork

This was disabled by a0da6deeec (ci: only run win+VS build & tests in
Git for Windows' fork, 2022-12-19) to avoid other forks doing too many
builds. But we want to keep these builds for the microsoft/git fork.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>

.github/workflows/main.yml

@@ -147,7 +147,7 @@ jobs:
   vs-build:
     name: win+VS build
     needs: ci-config
-    if: github.event.repository.owner.login == 'git-for-windows' && needs.ci-config.outputs.enabled == 'yes'
+    if: github.event.repository.owner.login == 'microsoft' && needs.ci-config.outputs.enabled == 'yes'
     env:
       NO_PERL: 1
       GIT_CONFIG_PARAMETERS: "'user.name=CI' 'user.email=ci@git'"