Linter: Fix false positives for pattern matching in erb-no-unused-literals

[markokajzer]

Rightward and one-line pattern matching were reported as unused literals, because the hash pattern keys were visited as symbol literals:

<% summary => { diff_count:, coding_import_form_result_id: } %>

Avoid using silent ERB tags for literals. `diff_count:` is evaluated but never used or output.

The rule now only visits the value being matched for => and in, not the pattern. A literal as the matched value (<% "a" => { size: } %>) is still reported.

[marcoroth]

Thanks @markokajzer!

Looks like at least somebody is using rightwards assignments in ERB files 🙈