RCORE-1990 Fix packaging for windows (#7762)

Author: jbreams

evergreen/config.yml

@@ -761,7 +761,7 @@ tasks:
         fi
 
         cd build
-        $CPACK -C ${cmake_build_type|Debug} -G TGZ -D "CPACK_PACKAGE_FILE_NAME=realm-core-artifacts" ${package_flags|}
+        "$CPACK" -C ${cmake_build_type|Debug} -G TGZ -D "CPACK_PACKAGE_FILE_NAME=realm-core-artifacts" ${package_flags|}
   - command: s3.put
     params:
       aws_key: '${artifacts_aws_access_key}'