fix: type error in the code used in the benchmark

The code comes from the LSP logfile, rather than the file on disk.

Author: david-christiansen

tests/bench/identifier_completion_didOpen.log

@@ -1,3 +1,3 @@
-Content-Length: 992
+Content-Length: 996
 
-{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"file:///home/mhuisi/Lean/lean4/tests/bench/identifier_completion.lean","languageId":"lean4","version":952,"text":"prelude\nimport Lean.AddDecl\n\nopen Lean\n\nset_option debug.skipKernelTC true\n\ndef buildSyntheticEnv : Lean.CoreM Unit := do\n  for i in [0:100000] do\n    let name := s!\"Long.And.Hopefully.Unique.Name.foo{i}\".toName\n    addDecl <| Declaration.opaqueDecl {\n      name := name\n      levelParams := []\n      type := .const `Nat []\n      value := .const `Nat.zero []\n      isUnsafe := false\n      all := [name]\n    }\n    addDocString name \"A synthetic doc-string\"\n\n#eval buildSyntheticEnv\n\n-- This will be quite a bit slower than the equivalent in a file that imports all of these decls,\n-- since we can pre-compute information about those imports.\n-- It still serves as a useful benchmark, though.\n#eval Long.And.Hopefully.Unique.Name.foo\n"},"dependencyBuildMode":"never"}}
+{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"file:///home/mhuisi/Lean/lean4/tests/bench/identifier_completion.lean","languageId":"lean4","version":952,"text":"prelude\nimport Lean.AddDecl\n\nopen Lean\n\nset_option debug.skipKernelTC true\n\ndef buildSyntheticEnv : Lean.CoreM Unit := do\n  for i in [0:100000] do\n    let name := s!\"Long.And.Hopefully.Unique.Name.foo{i}\".toName\n    addDecl <| Declaration.opaqueDecl {\n      name := name\n      levelParams := []\n      type := .const `Nat []\n      value := .const `Nat.zero []\n      isUnsafe := false\n      all := [name]\n    }\n    addDocStringCore name \"A synthetic doc-string\"\n\n#eval buildSyntheticEnv\n\n-- This will be quite a bit slower than the equivalent in a file that imports all of these decls,\n-- since we can pre-compute information about those imports.\n-- It still serves as a useful benchmark, though.\n#eval Long.And.Hopefully.Unique.Name.foo\n"},"dependencyBuildMode":"never"}}