Do not lint reused variable in trap

[A4-Tacks]

For bugs with existing features

• Rule Id (if any, e.g. SC1000): SC2064
• My shellcheck version (shellcheck --version or "online"): 0.10.0
• The rule's wiki page does not already cover this (e.g. https://shellcheck.net/wiki/SC2086)
• I tried on https://www.shellcheck.net/ and verified that this is still a problem on the latest commit

Here's a snippet or screenshot that shows the problem:

#!/bin/bash
trap "rm ${DIR@Q}" int

Here's what shellcheck currently says:

In - line 2:
trap "rm ${DIR@Q}" int
         ^------^ SC2064 (warning): Use single quotes, otherwise this expands now rather than when signalled.

Here's what I wanted or expected to see:

No warnings