Fix gen-release-notes script

We now only include the version in the release title, with the date below it. Because of this, need to adjust the script to understand the underlines that define the title are now shorter.

Author: nicoddemus

scripts/gen-release-notes.py

@@ -18,7 +18,7 @@
 capture = False
 for line in rst_text.splitlines():
     # Only start capturing after the latest release section.
-    if line.startswith("-------"):
+    if line.startswith("----"):
         capture = not capture
         if not capture:
             # We only need to capture the latest release, so stop.