update permissions samples on testing.md

[kuboon]

I was confused by the permissions option in Deno.test, so I’d like to suggest a correction.

In the early example, permissions: { read: true }, is included, but the test actually passes even without it. I found this point unclear, so I think it should be removed.

A more detailed explanation is provided in the ## Tests and Permissions section, but including the unnecessary permissions: { read: true }, there as well makes the line "allows you to specifically deny permissions, but does not grant them." harder to understand.

What do you think?