Update index.yml

Step 1: What is changing in this MR?

This MR adds Vueday 2023 conference to the events list and provides information about the talks Natalia Tepluhina and Anna Vovchenko are performing there.

Step 2: Ensure that your changes comply with the following, where applicable:

• I, the Assignee, have run Axe tools on any updated pages, and fixed the relevant accessibility issues.
• These changes meet a specific OKR or item in our Quarterly Plan.
• These changes work on both Safari, Chrome, and Firefox.
• These changes have been reviewed for Visual Quality Assurance and Functional Quality Assurance on Mobile, Desktop, and Tablet.
• These changes work with our Google Analytics and SEO tools.
• These changes have been documented as expected.

Step 3: Add the appropriate labels for triage

This MR will have dex-approval::2-standard automatically applied, but please update it as follows. If deciding between two levels, go with the higher of the two: https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/sites/handbook/source/handbook/marketing/digital-experience/marketing-site-approval-process/index.html.md

Step 4: Tag the appropriate person for review

Depending on which label is used, you may tag the following people as a Reviewer on this MR: https://about.gitlab.com/handbook/marketing/digital-experience/marketing-site-approval-process/#step-3-tag-the-appropriate-people-for-review