Automated update to Github CI to rustc nightly-2025-12-20

Update Nightly Rustc Bot · Update Nightly Rustc Bot · commit d1d90c0d10a7 · 2025-12-22T00:41:47.000Z
diff --git a/nightly-version b/nightly-version
@@ -1 +1 @@
-nightly-2025-09-27
+nightly-2025-12-20
