transaction: raise on backup restoration error stable

transaction: raise on backup restoration error

A few line above, similar errors in the truncation code result in raising the
associated exception. We should do the same here.

This means the transaction recover is more strict now, which might be a problem
when running `hg recover` in a share different from the one where the
transaction fails. However this has always been a problem and need to be be
addressed independently.

--- a/mercurial/transaction.py	Wed Mar 15 12:08:05 2023 +0100
+++ b/mercurial/transaction.py	Wed Mar 15 12:13:08 2023 +0100
@@ -145,6 +145,7 @@
                 except IOError as exc:
                     e_msg = stringutil.forcebytestr(exc)
                     report(_(b"failed to recover %s (%s)\n") % (f, e_msg))
+                    raise
             else:
                 target = f or b
                 try: