docs(star-history): make the chart taller (#11173)

Change the matplotlib figure size from (10, 4) to (10, 6) so the
star history chart renders vertically longer in the README. The
regenerated note/star_history.svg reflects the new 5:3 aspect ratio
(720x432pt) instead of the previous flat 2.5:1 (720x288pt).

.github/scripts/star_history.py

@@ -60,7 +60,7 @@ def fetch_stargazers():
 def render(stars, out):
     stars.sort()
     counts = list(range(1, len(stars) + 1))
-    fig, ax = plt.subplots(figsize=(10, 4), dpi=130)
+    fig, ax = plt.subplots(figsize=(10, 6), dpi=130)
     ax.plot(stars, counts, color="#0969da", linewidth=1.6)
     ax.set_xlabel("Date")
     ax.set_ylabel("Stars")