Windows CI: Add make install step on the shared 64 bit build

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/15433)

.github/workflows/windows.yml

@@ -33,6 +33,13 @@ jobs:
     - name: test
       working-directory: _build
       run: nmake test VERBOSE_FAILURE=yes TESTS=-test_fuzz
+    - name: install
+      # Run on 64 bit only as 32 bit is slow enough already
+      if: $${{ matrix.arch == 'win64' }}
+      run: |
+        mkdir _dest
+        nmake install DESTDIR=_dest
+      working-directory: _build
   plain:
     runs-on: windows-latest
     steps: