Bump core from 6a0458c to 12a5605 (#1718)

Bumps [core](https://github.com/microsoft/typespec) from `6a0458c` to
`12a5605`.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/microsoft/typespec/commit/12a560559b173468176a4d57436964b70a7a6e27"><code>12a5605</code></a>
Fix serialization of properties customized to be framework types (<a
href="https://redirect.github.com/microsoft/typespec/issues/4812">#4812</a>)</li>
<li><a
href="https://github.com/microsoft/typespec/commit/b33fe857f4b8f7d6fbfbdfacb9677f0c88371e59"><code>b33fe85</code></a>
[http-client-csharp] Fix: remove setters for props in readonly structs
(<a
href="https://redirect.github.com/microsoft/typespec/issues/4809">#4809</a>)</li>
<li><a
href="https://github.com/microsoft/typespec/commit/1a276608036a81d4cbca317d029e0f99a9ee28b7"><code>1a27660</code></a>
Responsive header (<a
href="https://redirect.github.com/microsoft/typespec/issues/4800">#4800</a>)</li>
<li><a
href="https://github.com/microsoft/typespec/commit/a8c67ff628e8c3c0a98dd0b69b899a8b7ae17768"><code>a8c67ff</code></a>
[http-client-csharp] Fix: allow suppressing &amp; replacing fields (<a
href="https://redirect.github.com/microsoft/typespec/issues/4795">#4795</a>)</li>
<li><a
href="https://github.com/microsoft/typespec/commit/48d7bc0cd22a6adf2a8c8affa63fc133b3a9ade3"><code>48d7bc0</code></a>
Generate raw data field as readonly (<a
href="https://redirect.github.com/microsoft/typespec/issues/4808">#4808</a>)</li>
<li><a
href="https://github.com/microsoft/typespec/commit/1b266e4bf8e3e90c5063419d2fb00892a55c3c6a"><code>1b266e4</code></a>
Fix decorator docs (<a
href="https://redirect.github.com/microsoft/typespec/issues/4785">#4785</a>)</li>
<li><a
href="https://github.com/microsoft/typespec/commit/bf632a7f24464da9032b2a6b6f0629a4b9e39fd2"><code>bf632a7</code></a>
[<code>@​typespec/http-specs</code>] - Modify code to handle
http-client-* packages tests (...</li>
<li><a
href="https://github.com/microsoft/typespec/commit/bb7d035c56fc08ee83ab301d214091d6e1a11179"><code>bb7d035</code></a>
Add blog back to astro (<a
href="https://redirect.github.com/microsoft/typespec/issues/4797">#4797</a>)</li>
<li><a
href="https://github.com/microsoft/typespec/commit/642a1d3e3360551c21ce32cb5463589eeac673bc"><code>642a1d3</code></a>
Fix publishing to github pages (<a
href="https://redirect.github.com/microsoft/typespec/issues/4801">#4801</a>)</li>
<li>See full diff in <a
href="https://github.com/microsoft/typespec/compare/6a0458c3fc363fcacd50e2f81dd899e40e962271...12a560559b173468176a4d57436964b70a7a6e27">compare
view</a></li>
</ul>
</details>
<br />


Dependabot will resolve any conflicts with this PR as long as you don't
alter it yourself. You can also trigger a rebase manually by commenting
`@dependabot rebase`.

[//]: # (dependabot-automerge-start)
[//]: # (dependabot-automerge-end)

---

<details>
<summary>Dependabot commands and options</summary>
<br />

You can trigger Dependabot actions by commenting on this PR:
- `@dependabot rebase` will rebase this PR
- `@dependabot recreate` will recreate this PR, overwriting any edits
that have been made to it
- `@dependabot merge` will merge this PR after your CI passes on it
- `@dependabot squash and merge` will squash and merge this PR after
your CI passes on it
- `@dependabot cancel merge` will cancel a previously requested merge
and block automerging
- `@dependabot reopen` will reopen this PR if it is closed
- `@dependabot close` will close this PR and stop Dependabot recreating
it. You can achieve the same result by closing it manually
- `@dependabot show <dependency name> ignore conditions` will show all
of the ignore conditions of the specified dependency
- `@dependabot ignore this major version` will close this PR and stop
Dependabot creating any more for this major version (unless you reopen
the PR or upgrade to it yourself)
- `@dependabot ignore this minor version` will close this PR and stop
Dependabot creating any more for this minor version (unless you reopen
the PR or upgrade to it yourself)
- `@dependabot ignore this dependency` will close this PR and stop
Dependabot creating any more for this dependency (unless you reopen the
PR or upgrade to it yourself)


</details>

---------

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Timothee Guerin <[email protected]>