chore: add Golang Serbia meetup to events page (gnolang#2163)

<!-- please provide a detailed description of the changes made in this
pull request. -->

## Description

This PR adds the Golang Serbia Gno meetup to the "Upcoming events" page
on `gnoweb`.

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

examples/gno.land/r/gnoland/pages/page_events.gno

@@ -17,6 +17,17 @@ We’re looking to connect with developers and like-minded thinkers who can cont
 
 <div class="column">
 
+### Gno @ Golang Serbia
+
+- Join the meetup
+- Belgrade, May 23, 2024
+
+[Learn more](https://www.meetup.com/golang-serbia/events/300975006/)
+
+</div><!-- end column-->
+
+<div class="column">
+
 ### GopherCon EU
 - Come Meet Us at our Booth
 - Berlin, June 17 - 20, 2024
@@ -43,6 +54,12 @@ We’re looking to connect with developers and like-minded thinkers who can cont
 [Learn More](https://nebular.builders/)
 </div><!-- end column-->
 
+<div class="column">
+
+</div><!-- end column-->
+<div class="column">
+
+</div><!-- end column-->
 </div><!-- end columns-3-->
 
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