Devel::Peek: fix build warning

[tonycoz]

This was:

Peek.xs:415:1: warning: missing initializer for field ‘xop_dump’ of ‘XOP’ {aka ‘const struct custom_op’} [-Wmissing-field-initializers]
415 | };
| ^
In file included from ../../perl.h:4542,
from Peek.xs:3:
../../op.h:926:21: note: ‘xop_dump’ declared here
926 | void (*xop_dump)(pTHX_ const OP *o, struct Perl_OpDumpContext *ctx);
| ^~~~~~~~

---

• This set of changes requires a perldelta entry, and it is included.
• This set of changes requires a perldelta entry, and I need help writing it.
• [ x] This set of changes does not require a perldelta entry.

[jkeenan]

The place where this warning began to be admitted was here:

commit 1eab73a91a97030ed9ce247321dea85de835f830
Author:     Paul Evans <leonerd@leonerd.org.uk>
AuthorDate: Fri Sep 6 18:35:47 2024
Commit:     Paul Evans <leonerd@leonerd.org.uk>
CommitDate: Mon Sep 9 05:38:25 2024

    Add xop_dump field and integrate into op_dump()

The patch clears up the warning.