test: correct isinstance check in webhook integration test #302

Job	Run time
PR title check	4s
Docstrings checks / Docstrings checks	18s
Code checks / Actions lint check	30s
Code checks / Spell check	8s
Doc checks / Doc checks / Docs check	1m 20s
Code checks / Lint check / Lint check (3.12)	13s
Code checks / Lint check / Lint check (3.14)	10s
Code checks / Lint check / Lint check (3.11)	10s
Code checks / Lint check / Lint check (3.13)	14s
Tests / Unit tests / Unit tests (ubuntu-latest, 3.14)	42s
Tests / Unit tests / Unit tests (ubuntu-latest, 3.13)	42s
Tests / Unit tests / Unit tests (windows-latest, 3.11)	59s
Tests / Unit tests / Unit tests (windows-latest, 3.13)	53s
Code checks / Type check / Type check (3.11)	16s
Tests / Unit tests / Unit tests (ubuntu-latest, 3.12)	44s
Tests / Unit tests / Unit tests (windows-latest, 3.14)	1m 35s
Tests / Unit tests / Unit tests (ubuntu-latest, 3.11)	39s
Code checks / Type check / Type check (3.14)	16s
Code checks / Type check / Type check (3.12)	13s
Tests / Unit tests / Unit tests (windows-latest, 3.12)	1m 0s
Code checks / Type check / Type check (3.13)	12s
Tests / Integration tests / Integration tests (ubuntu-latest, 3.14)	1m 17s
Tests / Integration tests / Integration tests (ubuntu-latest, 3.11)	1m 7s
	13m 42s

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