ci: prevent Visual Studio Build failing due to stderr

Under certain circumstances, seemingly timing-related, it would appear
that the `Bundle artifact tar` step triggers a rebuild of
`GIT-VERSION-FILE` (which actually does not change, obviously) and
reports that to `stderr`. Traditionally, PowerShell interprets _any_
output to `stderr` as a sign that something failed.

Let's teach our Azure Pipeline to _not_ fail, simply by suppressing that
output.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

azure-pipelines.yml

@@ -190,7 +190,7 @@ jobs:
       if (!$?) { exit(1) }
       & git-sdk-64-minimal\usr\bin\bash.exe -lc @"
         mkdir -p artifacts &&
-        eval \"`$(make -n artifacts-tar INCLUDE_DLLS_IN_ARTIFACTS=YesPlease ARTIFACTS_DIRECTORY=artifacts | grep ^tar)\"
+        eval \"`$(make -n artifacts-tar INCLUDE_DLLS_IN_ARTIFACTS=YesPlease ARTIFACTS_DIRECTORY=artifacts 2>&1 | grep ^tar)\"
       "@
       if (!$?) { exit(1) }
     displayName: Bundle artifact tar