prevent memory leak with currentComponent by unsetting it in diffed

[JoviDeCroock]

fixes #3907

[coveralls]

Coverage: 99.548%. Remained the same when pulling 36c70aa on prevent-memory-leak into cc88ae6 on master.

[github-actions]

Size Change: +9 B (0%)

Total Size: 54.2 kB

Filename	Size	Change
compat/dist/compat.js	3.88 kB	+2 B (0%)
compat/dist/compat.module.js	3.82 kB	+3 B (0%)
compat/dist/compat.umd.js	3.95 kB	+4 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
debug/dist/debug.js	3 kB	0 B
debug/dist/debug.module.js	3.01 kB	0 B
debug/dist/debug.umd.js	3.08 kB	0 B
devtools/dist/devtools.js	231 B	0 B
devtools/dist/devtools.module.js	240 B	0 B
devtools/dist/devtools.umd.js	314 B	0 B
dist/preact.js	4.24 kB	0 B
dist/preact.min.js	4.26 kB	0 B
dist/preact.min.module.js	4.26 kB	0 B
dist/preact.min.umd.js	4.29 kB	0 B
dist/preact.module.js	4.25 kB	0 B
dist/preact.umd.js	4.31 kB	0 B
hooks/dist/hooks.js	1.49 kB	0 B
hooks/dist/hooks.module.js	1.52 kB	0 B
hooks/dist/hooks.umd.js	1.57 kB	0 B
jsx-runtime/dist/jsxRuntime.js	360 B	0 B
jsx-runtime/dist/jsxRuntime.module.js	326 B	0 B
jsx-runtime/dist/jsxRuntime.umd.js	441 B	0 B
test-utils/dist/testUtils.js	442 B	0 B
test-utils/dist/testUtils.module.js	444 B	0 B
test-utils/dist/testUtils.umd.js	526 B	0 B

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