fix(plugin-legacy): prevent failed to load module

[sapphi-red]

Description

#7644 changed legacy detection code to try{import(new URL(import.meta.url).href).catch(()=>1);}catch(e){}window.${detectModernBrowserVarName}=true;.
When import.meta and dynamic import is supported, a fetch to current location which normally returns html will be executed.
That fetch occurs Failed to load module script: Expected a JavaScript module script but the server responded with a MIME type of "text/html". Strict MIME type checking is enforced for module scripts per HTML spec. error.

Note that import('_') does not show any error. I'm not sure but maybe because _ is not a valid url.

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[patak-cat]

Oh, good one!