What does this implement/fix? Explain your changes.

This fixes a bug where the "taxonomy" field will return an error when queried if the field is set to not allow multiple selections, but has multiple selections stored.

This can happen when the field was configured to allow multiple selections, had data saved, then is later changed to be a single select, but the stored data is still multiple values in an array.

• FAILED TEST: https://github.com/wp-graphql/wpgraphql-acf/actions/runs/7353282668/job/20019062914#step:7:1822
• PASSING TESTS: https://github.com/wp-graphql/wpgraphql-acf/actions/runs/7353345038

Does this close any currently open issues?

Related to #133

Any other comments?

1. Create a "Taxonomy" field on an ACF Field Group assigned to an ACF Block
2. Set the field to "Multi Select"
3. Edit the block using the field, selecting multiple terms

4. Save the content

Here we can see 2 terms are saved:

5. Change the field back to "Select" (to only allow 1 value) but leave the content as-is, with 2 terms stored as the field's value.
6. Query for the field

BEFORE

There's an error:

AFTER

No error, but the response only contains 1 item

Which matches the UI of the Block now, and if the block is saved again will only save 1 value instead of multiple: