[browser] loadBootResource should not ask for `dotnetwasm` location before cache lookup

[pavelsavara]

Because

https://github.com/dotnet/aspnetcore/blob/22b8ebb68bf74371b038841ea461d74da03182b9/src/Components/WebAssembly/testassets/HostedInAspNet.Client/wwwroot/index.html#L21

will force real fetch.

That breaks caching tests in BootResourceCachingTest
https://github.com/dotnet/aspnetcore/blob/22b8ebb68bf74371b038841ea461d74da03182b9/src/Components/test/E2ETest/Tests/BootResourceCachingTest.cs#L18

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Issue Details

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Because

https://github.com/dotnet/aspnetcore/blob/22b8ebb68bf74371b038841ea461d74da03182b9/src/Components/WebAssembly/testassets/HostedInAspNet.Client/wwwroot/index.html#L21

will force real fetch.

That breaks caching tests in BootResourceCachingTest
https://github.com/dotnet/aspnetcore/blob/22b8ebb68bf74371b038841ea461d74da03182b9/src/Components/test/E2ETest/Tests/BootResourceCachingTest.cs#L18

Author:	pavelsavara
Assignees:	pavelsavara
Labels:	arch-wasm, os-browser
Milestone:	8.0.0