Preferred Chronostrat querycbx incorrectly filtered by biostrat=true

[emenslin]

Describe the bug
When creating a new chronostrat record, if you try to add a preferred chronostrat it's being filtered by biostrat=true, even when the base record doesn't have biostrat checked. Likely introduced by #8257 since that introduced the biostrat filtering, but could also be related to #8254.

To Reproduce
Steps to reproduce the behavior:

1. Open a new chronostrat record
2. Type in the Preferred Chronostrat field
3. See only records with Is biostrat=true appear

Expected behavior
It shouldn't be filtered or should only be filtered when biostrat=true

Screenshots
Main, there are several nodes in the chronostrat tree and only one biostrat, but only the biostrat appears:

08-05_12.57.mp4

7.12.0.7:

08-05_12.58.mp4

Please fill out the following information manually:

• OS: Windows 11
• Browser: Chrome
• Specify 7 Version: 7.12.1
• Database Name: ciscollections
• Collection name: Fossils
• User Name: spadmin
• URL: https://ciscollections20250919-main.test.specifysystems.org/specify/