Trim the migration guide to genuine v1-to-v2 breaking changes #3755

Job	Run time
checks / readme-snippets	16s
checks / pre-commit	1m 0s
checks / docs	1m 48s
checks / test (3.10, locked, windows-latest)	2m 0s
checks / test (3.11, locked, ubuntu-latest)	1m 27s
checks / test (3.11, lowest-direct, windows-latest)	1m 53s
checks / test (3.10, lowest-direct, windows-latest)	1m 54s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 32s
checks / test (3.11, locked, windows-latest)	1m 58s
checks / test (3.10, locked, ubuntu-latest)	2m 53s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 24s
checks / test (3.13, lowest-direct, windows-latest)	1m 56s
checks / test (3.14, locked, windows-latest)	2m 2s
checks / test (3.14, lowest-direct, windows-latest)	1m 46s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 27s
checks / test (3.14, locked, ubuntu-latest)	1m 19s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 34s
checks / test (3.13, locked, ubuntu-latest)	1m 16s
checks / test (3.12, locked, ubuntu-latest)	1m 15s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 19s
checks / test (3.12, lowest-direct, windows-latest)	1m 57s
checks / test (3.13, locked, windows-latest)	1m 46s
checks / test (3.12, locked, windows-latest)	1m 51s
all-green	5s
	37m 38s

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