Update lean-toolchain for testing leanprover/lean4#8405

leanprover-community-mathlib4-bot · leanprover-community-mathlib4-bot · commit 18d3a54b4337 · 2025-05-20T16:47:02.000Z
diff --git a/lean-toolchain b/lean-toolchain
@@ -1 +1 @@
-leanprover/lean4:nightly-2025-05-19
+leanprover/lean4-pr-releases:pr-release-8405

Original file line number	Diff line number	Diff line change
`@@ -1 +1 @@`
`1`		`-leanprover/lean4:nightly-2025-05-19`
	`1`	`+leanprover/lean4-pr-releases:pr-release-8405`