Update repositories.txt

[Arduino15]

Added the A15RGB library for easy RGB LED control.

[github-actions]

Hi @Arduino15.
Your pull request has been detected as something other than a Library Manager submission.
A maintainer will need to review it before it can be merged.

If you intended to submit a library, please check the instructions and update your pull request if necessary:
https://github.com/arduino/library-registry/blob/main/README.md#instructions

[Arduino15]

hello! Please add my library to the library manager.

[per1234]

Closing as duplicate of #6237.

@Arduino15 in the future please only create one pull request for each submission.

As was already clearly explained in the comment from the bot in your original pull request, the library was accepted and will soon be available for installation via Library Manager (it likely already is):

#6237 (comment)

Your submission has now been accepted! Thanks for your contribution to the Arduino Library Manager index.

The library(s) will be available for installation via Library Manager within a day's time.

You can check the logs from the Library Manager indexer for your library(s) here:
http://downloads.arduino.cc/libraries/logs/github.com/Arduino15/A15RGB/

When submitting requests to this repository, we expect library maintainers to pay attention to the comments that are made on your requests by the bot and by the human maintainers.

[Arduino15]

Hello! Thank you very much!