chore: bump toolchain to v4.29.0-rc6 (#789)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: kim-em

lake-manifest.json

@@ -5,7 +5,7 @@
    "type": "git",
    "subDir": null,
    "scope": "",
-   "rev": "8629a535d10cd7edfbf1a2c5cdfbaeee135a62cd",
+   "rev": "650d4104daeb660ff3cc46715602a664504e7785",
    "name": "plausible",
    "manifestFile": "lake-manifest.json",
    "inputRev": "main",

lean-toolchain

@@ -1 +1 @@
-leanprover/lean4:v4.29.0-rc4
+leanprover/lean4:v4.29.0-rc6

test-projects/website/DemoSite/Blog/Conditionals.lean

@@ -257,7 +257,7 @@ example : (123123190283102938019238098 * 1234124).toString.length > 14 := by
   [reduction] unfolded reducible declarations (max: 46, num: 1):
     [reduction] outParam ↦ 46
   [type_class] used instances (max: 54, num: 1):
-    [type_class] USize.instOfNat ↦ 54
+    [type_class] Lean.Grind.CommRing.OfCommSemiring.instOfNatQ ↦ 54
   [reduction] Axioms (possibly imported non-exposed defs) that were tried to be unfolded (max: 22, num: 1):
     [reduction] sorryAx ↦ 22
   use `set_option diagnostics.threshold <num>` to control threshold for reporting counters