Fix useSyncExternalStore not working with function values

[marvinhagemeister]

When the value returned by the getSnapshot argument is a function we were calling that immediately instead of passing the function as a value around. This was caused by useState having the updater functionality, where a function is interpreted as being an updater function which allows you to optionally cancel a state update. But we don't want that here, we want the function itself to be preserved as a value.

Fixes #3632

[coveralls]

Coverage remained the same at 99.458% when pulling 482d3f6 on snapshot-function-values into 1a134b3 on master.

[github-actions]

Size Change: +6 B (0%)

Total Size: 43.5 kB

Filename	Size	Change
compat/dist/compat.js	3.67 kB	+2 B (0%)
compat/dist/compat.module.js	3.65 kB	+2 B (0%)
compat/dist/compat.umd.js	3.73 kB	+2 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
debug/dist/debug.js	3 kB	0 B
debug/dist/debug.module.js	3 kB	0 B
debug/dist/debug.umd.js	3.08 kB	0 B
devtools/dist/devtools.js	230 B	0 B
devtools/dist/devtools.module.js	238 B	0 B
devtools/dist/devtools.umd.js	305 B	0 B
dist/preact.js	4 kB	0 B
dist/preact.min.js	4.03 kB	0 B
dist/preact.module.js	4.02 kB	0 B
dist/preact.umd.js	4.06 kB	0 B
hooks/dist/hooks.js	1.31 kB	0 B
hooks/dist/hooks.module.js	1.33 kB	0 B
hooks/dist/hooks.umd.js	1.4 kB	0 B
jsx-runtime/dist/jsxRuntime.js	317 B	0 B
jsx-runtime/dist/jsxRuntime.module.js	327 B	0 B
jsx-runtime/dist/jsxRuntime.umd.js	395 B	0 B
test-utils/dist/testUtils.js	444 B	0 B
test-utils/dist/testUtils.module.js	444 B	0 B
test-utils/dist/testUtils.umd.js	521 B	0 B

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