AxisRegistry segfault

### What happened?

AxisRegistry segfault after merge (values are modified in place, the hash is not updated)

### What are the steps to reproduce the bug?

run fdb-axis on Lumi databridge 

### Version

5.13.*

### Platform (OS and architecture)

Linux (irrelevant)

### Relevant log output

_No response_

### Accompanying data

_No response_

### Organisation

_No response_