fix: tolerate <details> blocks without a summary when re-parsing release pull request bodies

[johnitvn]

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Fixes #2884 🦕

---

Problem

extractMultipleReleases() re-parses release pull request bodies with node-html-parser. A commit subject may legitimately contain a token like `<details>` inside an inline code span (which htmlEscape() intentionally leaves untouched, see #2801). The HTML parser does not understand markdown, so that token becomes a real <details> element without a <summary> child, and the current code dereferences it unconditionally:

const summaryNode = detail.getElementsByTagName('summary')[0];
const summary = summaryNode?.textContent;
const match = summary.match(SUMMARY_PATTERN); // TypeError when no <summary>

This hard-crashes every subsequent release-please run (Cannot read properties of undefined (reading 'match')) until someone merges or manually edits the open release pull request. Reproduction and full stack trace in #2884; observed in the wild on 17.6.0 and verified still present in 17.11.1.

Fix

Skip <details> blocks that have no <summary>, with a warning:

const summaryNode = detail.getElementsByTagName('summary')[0];
if (!summaryNode) {
  logger.warn(
    'found a <details> block without a <summary>, skipping it - ...'
  );
  continue;
}

Generated blocks always carry a <summary>, so real multi-component parsing is unchanged. For single-package bodies containing such a stray token, extraction now correctly falls back to the existing single-release path instead of throwing.

Tests

• should tolerate a <details> element missing a <summary> - a body whose changelog bullet contains a backticked <details> token parses to one release via the fallback path (previously crashed with exactly the reported TypeError)
• should keep parsing valid components around a <details> element missing a <summary> - injecting a stray summary-less block into the multi-component fixture still yields all valid components
• Full suite: 1211 passing, gts check clean, coverage not decreased

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[johnitvn]

I have already signed the CLA.