fix(Cache): print ProofWidgets build stdout on error (leanprover-community#33651)

Fixes a typo in the code for printing the output of failed `lake build` of the ProofWidgets fetch in `lake exe cache`. It will no properly print stdout rather than stderr under the `lake stdout:` heading.

Co-authored-by: Kim Morrison <kim@tqft.net>

Author: tydeu

Cache/Requests.lean

@@ -466,7 +466,7 @@ where
   printLakeOutput out := do
     unless out.stdout.isEmpty do
       IO.eprintln "lake stdout:"
-      IO.eprint out.stderr
+      IO.eprint out.stdout
     unless out.stderr.isEmpty do
       IO.eprintln "lake stderr:"
       IO.eprint out.stderr