Adjust script for getting changes to put in release notes

Now, this script is only useful for the preview channel's releases. The
stable channel's release notes can be mostly copied from the existing
preview releases notes.

Co-authored-by: Joseph Lyons <joseph@zed.dev>

script/get-preview-channel-changes

@@ -8,14 +8,14 @@ const FIXES_REGEX = /(fixes|closes) (.+[/#]\d+.*)$/im;
 main();
 
 async function main() {
-  // Get the last two tags
+  // Get the last two preview tags
   const [newTag, oldTag] = execFileSync(
     "git",
     ["tag", "--sort", "-committerdate"],
     { encoding: "utf8" }
   )
     .split("\n")
-    .filter((t) => t.startsWith("v"));
+    .filter((t) => t.startsWith("v") && t.endsWith('-pre'));
 
   // Print the previous release
   console.log(`Changes from ${oldTag} to ${newTag}\n`);
@@ -49,9 +49,28 @@ async function main() {
     .filter((line) => line.length > 0)
     .map((line) => line.match(PR_REGEX)[1]);
 
+  // Get the PRs that were cherry-picked between main and the old tag.
+  const existingPullRequestNumbers = new Set(execFileSync(
+    "git",
+    [
+      "log",
+      `main..${oldTag}`,
+      "--oneline",
+      "--grep",
+      "Merge pull request",
+    ],
+    { encoding: "utf8" }
+  )
+    .split("\n")
+    .filter((line) => line.length > 0)
+    .map((line) => line.match(PR_REGEX)[1]));
+    
+  // Filter out those existing PRs from the set of new PRs.
+  const newPullRequestNumbers = pullRequestNumbers.filter(number => !existingPullRequestNumbers.has(number));
+
   // Fetch the pull requests from the GitHub API.
   console.log("Merged Pull requests:")
-  for (const pullRequestNumber of pullRequestNumbers) {
+  for (const pullRequestNumber of newPullRequestNumbers) {
     const webURL = `https://github.com/zed-industries/zed/pull/${pullRequestNumber}`;
     const apiURL = `https://api.github.com/repos/zed-industries/zed/pulls/${pullRequestNumber}`;