Bump core from 89e19ef to 86cc361 (#1494)

Bumps [core](https://github.com/microsoft/typespec) from `89e19ef` to
`86cc361`.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/microsoft/typespec/commit/86cc361bf0a0ed29dbe80613cc2435331786cdce"><code>86cc361</code></a>
Add tests for changing property type/accessibility (<a
href="https://redirect.github.com/microsoft/typespec/issues/4365">#4365</a>)</li>
<li><a
href="https://github.com/microsoft/typespec/commit/782dca54ed80d8ecf92fc51d63f18b1906641aaf"><code>782dca5</code></a>
Support customizing property names (<a
href="https://redirect.github.com/microsoft/typespec/issues/4362">#4362</a>)</li>
<li><a
href="https://github.com/microsoft/typespec/commit/03d4fca5c0a99130616ccc2ae86ae30c6bee4bff"><code>03d4fca</code></a>
Improvements to type relation errors (<a
href="https://redirect.github.com/microsoft/typespec/issues/4357">#4357</a>)</li>
<li>See full diff in <a
href="https://github.com/microsoft/typespec/compare/89e19ef521ba988f5c4c18c8036b55d47206239d...86cc361bf0a0ed29dbe80613cc2435331786cdce">compare
view</a></li>
</ul>
</details>
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