Release notes tools: Improve grammar in list of backported commits

This commit improves the grammar when reporting which versions of
Blender a commit was backported to in the "bug fixes per major release"
script if it was backported to 3 or more verisons of Blender.

Before:
- Backported to 3.6.22 & 4.2.9 & 4.4.1

After:
- Backported to 3.6.22, 4.2.9, and 4.4.1

Along with this change, I now use the word "and" rather than the
symbol "&".

Pull Request: https://projects.blender.org/blender/blender/pulls/138500

release/release_notes/bug_fixes_per_major_release.py

@@ -426,8 +426,15 @@ class CommitInfo:
         formatted_string = (
             f" * {title} [[{self.hash[:11]}](https://projects.blender.org/blender/blender/commit/{self.hash})]"
         )
+
         if len(self.backport_list) > 0:
-            formatted_string += f" - Backported to {' & '.join(self.backport_list)}"
+            formatted_string += f" - Backported to "
+            if len(self.backport_list) > 2:
+                # In case of three or more backports, create a list that looks like:
+                # "Backported to 3.6, 4.2, and 4.3"
+                formatted_string += f"{', '.join(self.backport_list[:-1])}, and {self.backport_list[-1]}"
+            else:
+                formatted_string += " and ".join(self.backport_list)
         formatted_string += "\n"
 
         return formatted_string