[Misc] increase timeout for Win unittest to 50 mins. (#5973)

Co-authored-by: Ubuntu <ubuntu@ip-172-31-28-63.ap-northeast-1.compute.internal>

Jenkinsfile

@@ -81,7 +81,7 @@ def unit_test_cugraph(backend, dev) {
 def unit_test_win64(backend, dev) {
   init_git_win64()
   unpack_lib("dgl-${dev}-win64", dgl_win64_libs)
-  timeout(time: 30, unit: 'MINUTES') {
+  timeout(time: 50, unit: 'MINUTES') {
     bat "CALL tests\\scripts\\task_unit_test.bat ${backend}"
   }
 }