No errors if $SHELL is executed directly

[hyperupcall]

For bugs

• All versions
• 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:

# shellcheck shell=bash

$SHELL --version

$any_var --version

Here's what shellcheck currently says:

Nothing

Here's what I wanted or expected to see:

Expected to have error that $SHELL is not quoted. Although the value is usually /usr/bin/bash, it could very well be some long directory that includes whitespace.

No warnings show up for $any_var either - I suppose this was done because people combine the command path and its flags in the same variable and having a lint would cause more trouble than it's worth? Although I disagree, I'm not asking to change other variables since it's behavior is not unreasonable.