RFR: Adding latest talk to the list (JChampions 2026)

[María Arias de Reyna Domínguez]

Adding a new talk to the list of talks
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### Progress
- [x] Change must not contain extraneous whitespace

### Error
 ⚠️ The pull request body must not be empty.

### Reviewing
<details><summary>Using <code>git</code></summary>

Checkout this PR locally: \
`$ git fetch https://git.openjdk.org/leyden-docs.git pull/6/head:pull/6` \
`$ git checkout pull/6`

Update a local copy of the PR: \
`$ git checkout pull/6` \
`$ git pull https://git.openjdk.org/leyden-docs.git pull/6/head`

</details>
<details><summary>Using Skara CLI tools</summary>

Checkout this PR locally: \
`$ git pr checkout 6`

View PR using the GUI difftool: \
`$ git pr show -t 6`

</details>
<details><summary>Using diff file</summary>

Download this PR as a diff file: \
<a href="https://git.openjdk.org/leyden-docs/pull/6.diff">https://git.openjdk.org/leyden-docs/pull/6.diff</a>

</details>

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Commit messages:
 - Adding latest talk to the list (JChampions 2026)

Changes: https://git.openjdk.org/leyden-docs/pull/6/files
  Webrev: https://webrevs.openjdk.org/?repo=leyden-docs&pr=6&range=00
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/leyden-docs/pull/6.diff
  Fetch: git fetch https://git.openjdk.org/leyden-docs.git pull/6/head:pull/6

PR: https://git.openjdk.org/leyden-docs/pull/6