fix: correctly determine release to add to a channel

- Add only the most recent release to a channel (rather than adding all the one not added yet)
- Avoid attempting to ad the version twice in case that version is already present in multiple upper branches

lib/get-last-release.js

@@ -27,16 +27,17 @@ const {makeTag, isSameChannel} = require('./utils');
  * @return {LastRelease} The last tagged release or empty object if none is found.
  */
 module.exports = ({branch, options: {tagFormat}}, {before} = {}) => {
-  const [{version, gitTag, channel} = {}] = branch.tags
+  const [{version, gitTag, channels} = {}] = branch.tags
     .filter(
       tag =>
-        (branch.type === 'prerelease' && isSameChannel(branch.channel, tag.channel)) || !semver.prerelease(tag.version)
+        (branch.type === 'prerelease' && tag.channels.some(channel => isSameChannel(branch.channel, channel))) ||
+        !semver.prerelease(tag.version)
     )
     .filter(tag => isUndefined(before) || semver.lt(tag.version, before))
     .sort((a, b) => semver.rcompare(a.version, b.version));
 
   if (gitTag) {
-    return {version, gitTag, channel, gitHead: gitTag, name: makeTag(tagFormat, version)};
+    return {version, gitTag, channels, gitHead: gitTag, name: makeTag(tagFormat, version)};
   }
 
   return {};