SQL query from DB Manager is executed twice

[nextstopsun]

What is the bug or the crash?

When executing a query in DB Managers SQL Window, it's being sent to database twice.

Steps to reproduce the issue

Testing on postgres:

1. Open DB Manager SQL Window dialog.
2. Enter SQL query:

SELECT 'test'

3. Look into the database log.

2021-09-29 09:04:30.608 UTC [64] LOG:  statement: SET application_name='QGIS'
2021-09-29 09:04:30.610 UTC [64] LOG:  statement: SET extra_float_digits=3
2021-09-29 09:04:30.613 UTC [64] LOG:  statement: SELECT 'test'
2021-09-29 09:04:30.615 UTC [64] LOG:  statement: SELECT oid, typname FROM pg_type WHERE oid IN (25)
2021-09-29 09:04:30.626 UTC [64] LOG:  statement: SELECT 'test'
2021-09-29 09:04:30.628 UTC [64] LOG:  statement: SELECT oid, typname FROM pg_type WHERE oid IN (25)

Versions

Tested on 3.20.
Looks like 3.16 and above are affected.

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response

[Gustry]

Linked to #45204 ?

[gioman]

Linked to #45204 ?

I had the same thought.

[nextstopsun]

Linked to #45204 ?

Not only this slows down queries, but causes constraint violations in some cases.