chore(NODE-5547): fix npm version setting var (#633)

Author: nbbeeken

.evergreen/config.yml

@@ -101,8 +101,9 @@ tasks:
       - func: fetch source
         vars:
           NODE_LTS_VERSION: 14
-          NPM_VERSION: 9
       - func: install dependencies
+        vars:
+          NPM_VERSION: 9
       - func: run tests
         vars:
           TEST_TARGET: node