fix(util): preserve escaped angle brackets across merged-PR double parse

[sylwit]

Manifest.findMergedReleasePullRequests parses the merged release PR body once, then calls toString() on the result and hands that string to every Strategy.buildRelease, which parses it a second time. extractMultipleReleases read each section's notes with textContent, which decodes htmlEscape's </> back into a raw <word>. That raw tag survives into the reserialised body and breaks the second HTML parse, silently dropping whichever <details> section contains it (and any later sections nested inside it).

Read the notes with innerHTML instead: it preserves release-please's own escaping verbatim, so it round-trips through both parses without corrupting the DOM.

Fixes #2899

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Fixes #<issue_number_goes_here> 🦕

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