fix(tools/installer): Fix DENO_INSTALL_ROOT

[dovakin0007]

This PR fixes the issue where the PathBuf appends /bin even if bin dir already exists referenced in this issue
#26442

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[bartlomieju]

Is there a test you could that that exercises this change? You could put it in tests/integration/install_tests.rs

[dovakin0007]

Is there a test you could that that exercises this change? You could put it in tests/integration/install_tests.rs

let me try to do that then!

[dovakin0007]

Is there a test you could that that exercises this change? You could put it in tests/integration/install_tests.rs

should I create a new test case or modifying an existing test case is fine? right now I modified an existing test case

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