fix: fix unnamed dollar string detection (v7)

[ephys]

Pull Request Checklist

• Have you added new tests to prevent regressions?
• If a documentation update is necessary, have you opened a PR to the documentation repository?
• Did you update the typescript typings accordingly (if applicable)?
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Description Of Change

Fixes an issue reported here: #15301 (comment)

Basically unnamed $$ quoted strings were ending too quickly. The parser considered the string to be delimited like this:

SELECT $$ id $$
--     ^ start of string
--      ^ end of string

instead of this:

SELECT $$ id $$
--     ^ start of string
--           ^ end of string