ci: verify that the Git and Scalar executables work in Nano Server

It was reported in git-for-windows/git#4052
that Git for Windows v2.38.0 introduced a regression where `git.exe`
could no longer be run in Nano Server containers.

The issue was fixed in git-for-windows/git#4074

Let's add a workflow that verifies that Git for Windows does not regress
on this in the future.

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

Author: dscho

.github/workflows/nano-server.yml

@@ -0,0 +1,35 @@
+name: Windows Nano Server tests
+
+on: [workflow_dispatch, push]
+
+jobs:
+  test-nano-server:
+    if: github.event.repository.fork == false || github.event_name == 'workflow_dispatch'
+    runs-on: windows-2022
+    env:
+      REF: ${{github.ref}}
+      WINDBG_DIR: "C:/Program Files (x86)/Windows Kits/10/Debuggers/x64"
+      IMAGE: mcr.microsoft.com/powershell:nanoserver-ltsc2022
+
+    steps:
+      - name: partial clone
+        shell: bash
+        run: |
+          # cannot use `git clone` directly, to allow for PR's refs to be fetched
+          git clone --no-checkout --single-branch -b ${REF#refs/heads/} --filter=blob:none --depth=1 \
+            https://github.com/${{github.repository}} . &&
+          git sparse-checkout set .github/workflows mingw64/bin &&
+          git checkout HEAD
+      - name: pull nanoserver image
+        shell: bash
+        run: docker pull $IMAGE
+      - name: run nano-server test
+        shell: bash
+        run: |
+          docker pull $IMAGE
+          docker run \
+            --user "ContainerAdministrator" \
+            -v "$WINDBG_DIR:C:/dbg" \
+            -v "$(cygpath -aw mingw64/bin):C:/test" \
+            -v "$(cygpath -aw .github/workflows/nano-server):C:/script" \
+            $IMAGE pwsh.exe C:/script/run-tests.ps1

.github/workflows/nano-server/run-tests.ps1

@@ -0,0 +1,34 @@
+# Each exectuable to test is run with the `version` subcommand; It is
+# expected to return with exit code 0.
+
+$executables_to_test = @(
+    'C:\test\git.exe',
+    'C:\test\scalar.exe'
+)
+
+foreach ($executable in $executables_to_test)
+{
+    Write-Output "Now testing $($executable)"
+    &$executable 'version'
+    if ($LASTEXITCODE -ne 0) {
+	# If the command failed, run the debugger to find out what function or
+	# DLL could not be found and then exit the script with failure. The
+	# missing DLL or EXE will be referenced near the end of the output
+
+        # Set flag to ask the debugger to
+	# - show loader stub dianostics,
+	# - enable system critical breaks,
+	# - stop on exception, and
+	# - stop on unhandled user-mode exception
+	#
+	# For further details, see
+	# https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/gflags-flag-table
+        C:\dbg\gflags -i $executable +SLS +SCB +SOE +SUE
+
+        C:\dbg\cdb.exe -c "g" -c "q" $executable 'version'
+
+        exit 1
+    }
+}
+
+exit 0