chore(release): 5.2.0 (#24898)

Bumps `.release-please-manifest.json` on `v5-next` from **5.1.0 →
5.2.0** so v5-next nightlies track the next minor after v5.1.0 is cut.

One-line change, mirrors the previous bump (`ee3716277a chore(release):
5.1.0`). Independent of the v5.1.0 merge (#24897) — that branch is
frozen at 5.1.0.

If preferred, this can instead be applied via a bypass push with the
release bot and this PR closed.

Author: alexghr

.release-please-manifest.json

@@ -1,3 +1,3 @@
 {
-  ".": "5.1.0"
+  ".": "5.2.0"
 }