SearchKit - Fix updating Entity Ref fields

[colemanw]

Overview

Fix a couple bugs in SearchKit handling bulk-updates of Entity Ref fields.

Before

1. Create a custom field type Contact Reference.
2. Create a search, select one or more rows & choose "Update Contacts" from the Actions menu.
3. Select the custom field.

Problem 1: Field appears as an integer
Problem 2: Fixing first bug, then selecting "Current User" from the EntityRef widget will fail.

After

Both issues fixed.

[civibot]

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[seamuslee001]

Has a test and the code reads well makes sense to me merging