Fix typo in "how to handle errors" doc

Summary:
Fix typo in "how to handle errors" doc

join -> join_all

Reviewed By: JakobDegen

Differential Revision: D68369429

fbshipit-source-id: d89082a15dd692c564f8756ace37621c11c478cc

Author: Nero5023

docs/bxl/how_tos/how_to_handle_errors.md

@@ -62,15 +62,15 @@ lazy_ops = [
 #### For collective error handling (stop on first error):
 
 ```python
-result = ctx.lazy.join(lazy_ops).catch().resolve()
+result = ctx.lazy.join_all(lazy_ops).catch().resolve()
 ```
 
 The Return type is `Result[list[bxl.AnalysisResult]]`
 
 #### For individual error handling per operation:
 
 ```python
-result = ctx.lazy.join([op.catch() for op in lazy_ops]).resolve()
+result = ctx.lazy.join_all([op.catch() for op in lazy_ops]).resolve()
 ```
 
 The Return type is `list[Result[bxl.AnalysisResult]]`