add dummy entry to release-notes script for new pkg

The regex checks for existence of the previous h2
but new packages will not have versions before it.
Add a dummy h2 to satisfy the regex with minimal
overall changes.
To test this, replace Unreleased in the CHANGELOG
to an actual version, like 1.1.1.
Then run the script as described in the comments.
There should be a .tmp/release-notes.md with
the contents of the changelog for that version.

scripts/extract-latest-release-notes.js

@@ -6,6 +6,7 @@
  * - node scripts/extract-latest-release-notes.js [PATH TO CHANGELOG]...
  * Examples:
  * - node scripts/extract-latest-release-notes.js ./packages/CHANGELOG.md
+ * - node scripts/extract-latest-release-notes.js ./packages/opentelemetry-semantic-conventions/CHANGELOG.md
  * - node scripts/extract-latest-release-notes.js ./experimental/CHANGELOG.md
  * - node scripts/extract-latest-release-notes.js ./api/CHANGELOG.md ./packages/CHANGELOG.md ./experimental/CHANGELOG.md
  */
@@ -17,8 +18,8 @@ function extractLatestChangelog(changelogPath) {
   // Matches everything from the first entry at h2 ('##') followed by a space and a non-prerelease semver version
   // until the next entry at h2.
   const firstReleaseNoteEntryExp = /^## \d+\.\d+\.\d\n.*?(?=^## )/ms;
-
-  return changelog.match(firstReleaseNoteEntryExp)[0];
+  // append the changelog with a dummy entry to ensure new packages match the regex
+  return (changelog + '\n## ').match(firstReleaseNoteEntryExp)[0];
 }
 
 fs.mkdirSync('./.tmp/', {