MEMLEAK in test to reproduce issue `option_shutdown_anysegwit`

In a test to reproduce #9389 (PR #9390 )

two MEMLEAK occur:

```
**BROKEN** lightningd: MEMLEAK: 0x870c21e78
**BROKEN** lightningd: label=u8[]
**BROKEN** lightningd: alloc:
**BROKEN** lightningd: channeld/channeld_wiregen.c:1570 (fromwire_channeld_got_shutdown)
**BROKEN** lightningd: lightningd/channel_control.c:1300 (peer_got_shutdown)
**BROKEN** lightningd: lightningd/channel_control.c:1633 (channel_msg)
**BROKEN** lightningd: parents:
**BROKEN** lightningd: struct channel
```

and

```
**BROKEN** lightningd: MEMLEAK: 0x8710392e8
**BROKEN** lightningd: label=u8[]
**BROKEN** lightningd: alloc:
**BROKEN** lightningd: wire/peer_wiregen.c:2071 (towire_warning)
**BROKEN** lightningd: common/wire_error.c:55 (towire_warningfmtv)
**BROKEN** lightningd: common/wire_error.c:70 (towire_warningfmt)
**BROKEN** lightningd: lightningd/channel_control.c:1314 (peer_got_shutdown)
**BROKEN** lightningd: lightningd/channel_control.c:1633 (channel_msg)
**BROKEN** lightningd: parents:
```

Start with the test reproducing #9389 using option_shutdown_anysegwit, then inspect the reported paths in lightningd/channel_control.c, channeld/channeld_wiregen.c, wire/peer_wiregen.c, and common/wire_error.c. Trace ownership of the two u8[] allocations through peer_got_shutdown and channel_msg; done means the reproducer no longer reports either MEMLEAK.

Written by the indexing model from the issue text.