fix: correct MCPServer call_tool result type #2571

Job	Run time
checks / pre-commit	40s
checks / readme-snippets	11s
checks / test (3.11, lowest-direct, windows-latest)	1m 16s
checks / test (3.11, lowest-direct, ubuntu-latest)	49s
checks / test (3.10, locked, windows-latest)	1m 35s
checks / test (3.10, lowest-direct, windows-latest)	1m 9s
checks / test (3.14, lowest-direct, ubuntu-latest)	46s
checks / test (3.13, locked, windows-latest)	1m 11s
checks / test (3.10, lowest-direct, ubuntu-latest)	52s
checks / test (3.14, locked, ubuntu-latest)	1m 49s
checks / test (3.10, locked, ubuntu-latest)	52s
checks / test (3.13, lowest-direct, windows-latest)	1m 19s
checks / test (3.12, lowest-direct, ubuntu-latest)	58s
checks / test (3.12, locked, ubuntu-latest)	50s
checks / test (3.13, locked, ubuntu-latest)	44s
checks / test (3.12, locked, windows-latest)	1m 20s
checks / test (3.13, lowest-direct, ubuntu-latest)	49s
checks / test (3.14, lowest-direct, windows-latest)	1m 5s
checks / test (3.12, lowest-direct, windows-latest)	1m 26s
checks / test (3.11, locked, windows-latest)	1m 21s
checks / test (3.11, locked, ubuntu-latest)	49s
checks / test (3.14, locked, windows-latest)	2m 1s
all-green	3s
	23m 55s

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