Fix panic in testutil/validatormock/synccomm.go

[dB2510]

🐞 Bug Report

Description

A panic has been observed by compose tests in github actions: https://github.com/ObolNetwork/charon/actions/runs/5335228338/attempts/1
Might be due to a race condition.

Has this worked before in a previous version?

Yes

🔬 Minimal Reproduction

🔥 Error

panic: close of closed channel
�[35mnode2_1       |�[0m 
�[35mnode2_1       |�[0m goroutine 478 [running]:
�[35mnode2_1       |�[0m github.com/obolnetwork/charon/testutil/validatormock.(*SyncCommMember).setDuties(0x1d76ea0?, 0xc002d69c80?, {0x2a468b0?, 0xc001f4bd00?, 0x1d76ea0?})
�[35mnode2_1       |�[0m 	/app/charon/testutil/validatormock/synccomm.go:153 +0x105
�[35mnode2_1       |�[0m github.com/obolnetwork/charon/testutil/validatormock.(*SyncCommMember).PrepareEpoch(0xc001fc6b40, {0x1d76ea0, 0xc002d69c80})
�[35mnode2_1       |�[0m 	/app/charon/testutil/validatormock/synccomm.go:182 +0x9f
�[35mnode2_1       |�[0m github.com/obolnetwork/charon/app.wireValidatorMock.func1.2({0x1d76ea0?, 0xc002d69c80?}, {{0x1d92f00, 0xc001f4bd00}, 0xc001b0e600, 0xc001d94e70, 0xc001fc6b40})
�[35mnode2_1       |�[0m 	/app/charon/app/vmock.go:47 +0x45
�[35mnode2_1       |�[0m github.com/obolnetwork/charon/app.newVMockWrapper.func1.1()
�[35mnode2_1       |�[0m 	/app/charon/app/vmock.go:182 +0xac
�[35mnode2_1       |�[0m created by github.com/obolnetwork/charon/app.newVMockWrapper.func1
�[35mnode2_1       |�[0m 	/app/charon/app/vmock.go:178 +0x792

Anything else relevant (validator index / public key)?
Here's complete log of the failed test: run_version_matrix_with_dkg.log