test: mark test-npm-install flaky on arm

PR-URL: nodejs#14035
Refs: nodejs#14015
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/parallel.status

@@ -14,6 +14,7 @@ prefix parallel
 
 [$arch==arm || $arch==arm64]
 test-fs-readdir-ucs2 : PASS,FLAKY
+test-npm-install:      PASS,FLAKY
 
 [$system==solaris] # Also applies to SmartOS