magento/module-catalog/Setup/Patch/Data/UpdateMultiselectAttributesBackendTypes.php breaks upgrade in migrated sites from 1.x

Nobody has claimed this yet.

### Preconditions and environment

- 2.4.6-p2

### Steps to reproduce

To replicate this you need

1. Magento 2 (e.g. 2.4.1) that was migrated from 1.x and the 1.x instance had multiselect attributes with data (stored in _text table)
2. Use data migration tool to transfer the data which will copy the values from _text table to _varchar table during migration
3. Upgrade to 2.4.6-p2

The system will try to copy data from the _varchar table back to the _text table which was already migrated with the data migration tool to _text and to _varchar table. In the process you'll get this error about duplicate values

### Expected result

Upgrade occurs properly

### Actual result

Duplicated values throw exceptions


### Additional information

There is only one real solution here, the patch needs to first clear the invalid data from _text table before migrating from _varchar to _text

e.g.

```sql
delete from catalog_product_entity_text where catalog_product_entity_text.attribute_id in (select eav_attribute.attribute_id from eav_attribute where eav_attribute.backend_type = 'varchar' and eav_attribute.entity_type_id = 4)
```

### Release note

_No response_

### Triage and priority

- [ ] Severity: **S0** _- Affects critical data or functionality and leaves users without workaround._
- [X] Severity: **S1** _- Affects critical data or functionality and forces users to employ a workaround._
- [ ] Severity: **S2** _- Affects non-critical data or functionality and forces users to employ a workaround._
- [ ] Severity: **S3** _- Affects non-critical data or functionality and does not force users to employ a workaround._
- [ ] Severity: **S4** _- Affects aesthetics, professional look and feel, “quality” or “usability”._

Start with magento/module-catalog/Setup/Patch/Data/UpdateMultiselectAttributesBackendTypes.php and reproduce the upgrade on a migrated Magento 1.x site containing multiselect attribute data. Inspect the catalog_product_entity_text and catalog_product_entity_varchar records involved, then verify that the upgrade completes without duplicate-value exceptions and preserves the migrated data.

Written by the indexing model from the issue text.