Fix random panic bug

[xenowits]

🐞 Bug Report

Description

Random panic bugs are encountered when running smoke_internal_test.go. These panics are related to closing an already closed channel.

The error traces lead to SlotAttester's Prepare method and SyncComm's PrepareEpoch method.

Has this worked before in a previous version?

Yes.

🔬 Minimal Reproduction

Run "default beta" smoke test locally multiple times. Or perhaps run the test in a loop.

🔥 Error

1260052398-node2-1           | panic: close of closed channel
1260052398-node2-1           | 
1260052398-node2-1           | goroutine 461 [running]:
1260052398-node2-1           | github.com/obolnetwork/charon/testutil/validatormock.(*SyncCommMember).PrepareEpoch(0xc000137080, {0x1b23430, 0xc0002fc780})
1260052398-node2-1           | 	/Users/xenowits/obol/charon/testutil/validatormock/synccomm.go:130 +0x110
1260052398-node2-1           | github.com/obolnetwork/charon/app.wireValidatorMock.func1.2({0x1b23430?, 0xc0002fc780?}, {{0x1b3c8f0, 0xc001bf4760}, 0xc001d0a5a0, 0xc001ec7220, 0xc000137080})
1260052398-node2-1           | 	/Users/xenowits/obol/charon/app/vmock.go:59 +0x45
1260052398-node2-1           | github.com/obolnetwork/charon/app.newVMockWrapper.func1.1()
1260052398-node2-1           | 	/Users/xenowits/obol/charon/app/vmock.go:168 +0xac
1260052398-node2-1           | created by github.com/obolnetwork/charon/app.newVMockWrapper.func1
1260052398-node2-1           | 	/Users/xenowits/obol/charon/app/vmock.go:164 +0x5e5

🌍 Your Environment

Operating System:

  
macOS Monterey
Version 12.6
  

What version of Charon are you running? (Which release)

  
Locally built latest main
  

Anything else relevant (validator index / public key)?