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GH-36858: [Go] Fix dictionary builder leak (#36859)



### Rationale for this change

This fixes a potential leak when using a memory allocator that can panic.

### What changes are included in this PR?

This moves the `Retain` call to happen after the last potential allocation in `newWithDictOffset` to prevent a leak.

### Are these changes tested?

A unit test was added that causes the builder to panic on the `GetDictArrayData` step.

### Are there any user-facing changes?

* Closes: #36858

Authored-by: thorfour <me@thor-hansen.com>
Signed-off-by: Matt Topol <zotthewizard@gmail.com>