Add section about Constrained classes to the Migration Guide #9555

Job	Run time
test fastapi	2m 20s
lint 3.7	1m 31s
lint 3.8	1m 19s
lint 3.9	1m 9s
lint 3.10	1m 42s
lint 3.11	2m 4s
docs-build	1m 24s
test ubuntu / 3.7	2m 43s
test ubuntu / 3.8	1m 59s
test ubuntu / 3.9	2m 54s
test ubuntu / 3.10	2m 13s
test ubuntu / 3.11	2m 38s
test macos / 3.7	2m 57s
test macos / 3.8	3m 1s
test macos / 3.9	3m 17s
test macos / 3.10	3m 32s
test macos / 3.11	3m 18s
test windows / 3.7	3m 40s
test windows / 3.8	3m 7s
test windows / 3.9	3m 35s
test windows / 3.10	4m 40s
test windows / 3.11	3m 44s
test ubuntu / pypy3.7	7m 42s
test ubuntu / pypy3.8	7m 43s
test ubuntu / pypy3.9	11m 21s
test memray	5m 25s
mypy 1.0.1 / 3.10	4m 37s
mypy lockfile / 3.10	4m 4s
mypy 1.2.0 / 3.10	4m 37s
mypy 1.4.1 / 3.10	4m 7s
mypy lockfile / 3.7	4m 36s
mypy lockfile / 3.8	3m 42s
mypy lockfile / 3.9	3m 30s
mypy lockfile / 3.11	2m 45s
test typing-extensions 4.6.1 on Python 3.8	2m 15s
test typing-extensions 4.6.1 on Python 3.9	2m 50s
test typing-extensions 4.6.1 on Python 3.10	2m 30s
test typing-extensions 4.6.1 on Python 3.11	2m 43s
test typing-extensions main on Python 3.8	2m 23s
test typing-extensions main on Python 3.9	2m 59s
test typing-extensions main on Python 3.10	2m 56s
test typing-extensions main on Python 3.11	2m 28s
test typing-extensions 4.6.1 on Python 3.7	1m 22s
coverage-combine	27s
check	2s
release	0s
Send tweet	0s
	2h 25m 51s

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