test: fix error when foo in path to git clone

I fixed an error that occured in the test case of the file
test/parallel/test-assert-fail.js when foo was in the path to
the git clone. This occured due to a regex that looked only for the
word foo, and so it was updated to not look for foo/, but only
foo. This way it won't go off from foo being in the path to the
git clone

PR-URL: #14506
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>

test/parallel/test-assert-fail.js

@@ -67,5 +67,5 @@ common.expectsError(() => {
 // The stackFrameFunction should exclude the foo frame
 assert.throws(
   function foo() { assert.fail('first', 'second', 'message', '!==', foo); },
-  (err) => !/foo/m.test(err.stack)
+  (err) => !/^\s*at\sfoo\b/m.test(err.stack)
 );