[MC-279551] Test blocks and test instance blocks broken by Wither

Withers can destroy test blocks and test instance blocks.

Steps to Reproduce:

1. Create an area of test blocks/test instance blocks

2. Summon a wither and hit it

3. The test blocks/test instance blocks around the wither are broken

Linked issues

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We're tracking this issue in MC-279498, so this ticket is being resolved and linked as a duplicate.

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