fix: only destroy snippets when they have changed

[Rich-Harris]

Fixes #11266. For the life of me I can't reproduce the bug in our test suite — I've been tearing my hair out for a while, and can't afford to waste any more time on it — and as such there's no test with this PR.

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[dummdidumm]

Is it a dev only bug maybe? In that case, maybe compilerOptions: { dev: true } helps

[Rich-Harris]

I had the same thought but it made no difference and I gave up

[dummdidumm]

compilerOptions: { accessors: false } (because IIRC they're enabled by default in the test suite)?