pw_build: Fix exception handling in mirror_tree

When linking fails, we fall back to copying. This always fails because
the original reception is re-raised even if the copy succeeds.

Just remove the exception management in the copy case. If copying fails,
we'll get both exceptions reported in a chain.

No-Docs-Update-Reason: bug fix
Change-Id: I49f0b381ba0e607f46725d1cd59bb16b811c7cf2
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/48700
Commit-Queue: Michael Spang <spang@google.com>
Reviewed-by: Rob Mohr <mohrr@google.com>

pw_build/py/pw_build/mirror_tree.py

diff --git a/pw_build/py/pw_build/mirror_tree.py b/pw_build/py/pw_build/mirror_tree.py
index a1a74b2..46d19a0 100644
--- a/pw_build/py/pw_build/mirror_tree.py
+++ b/pw_build/py/pw_build/mirror_tree.py
@@ -63,12 +63,8 @@
         # If the link failed try copying. If copying fails re-raise the
         # original exception.
         except OSError:
-            try:
-                shutil.copy(source, dest)
-                yield dest
-            except OSError:
-                pass
-            raise
+            shutil.copy(source, dest)
+            yield dest
 
 
 def _link_files_or_dirs(paths: Iterable[Path],