use closeImmediatly()

[koppor]

Follow-up to #11845

Hopefully fixes OutOfMemoryExceptions

Tries to make use of closeImmediatly() of MVStore

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• [/] Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• [/] Tests created for changes (if applicable)
• [/] Manually tested changed features in running JabRef (always required)
• [/] Screenshots added in PR description (if change is visible to the user)
• [/] Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• [/] Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

Maybe refs h2database/h2database#4233

[trag-bot]

@trag-bot didn't find any issues in the code! ✅✨

[koppor]

Did not fix. Out of context now. Closing.