Update README.md with GitHub actions Ubuntu CI nightly (#4979)

Signed-off-by: JesusPoderoso <jesuspoderoso@eprosima.com>
(cherry picked from commit 1409dc2)

README.md

@@ -28,7 +28,7 @@
     <a href="https://eprosima-fast-rtps.readthedocs.io"><img alt="Documentation badge" src="https://img.shields.io/readthedocs/eprosima-fast-rtps.svg"/></a>
     <br>
     <a href=""><img alt="Status" src="https://nexus.lab.fiware.org/static/badges/statuses/incubating.svg"/></a>
-    <a href="http://jenkins.eprosima.com:8080/job/nightly_fastdds_sec_master_linux"><img alt="Linux ci" src="http://jenkins.eprosima.com:8080/job/nightly_fastdds_sec_master_linux/lastCompletedBuild/badge/icon?subject=%20%20%20Linux%20CI%20"/></a>
+    <a href="https://github.com/eProsima/Fast-DDS/actions/workflows/nightly-ubuntu-ci.yml"><img alt="Fast DDS Ubuntu CI (nightly)" src="https://github.com/eProsima/Fast-DDS/actions/workflows/nightly-ubuntu-ci.yml/badge.svg"/></a>
     <a href="http://jenkins.eprosima.com:8080/view/Nightly/job/nightly_fastdds_sec_master_linux_aarch64/"><img alt="Linux arm64 ci" src="http://jenkins.eprosima.com:8080/job/nightly_fastdds_sec_master_linux_aarch64/lastCompletedBuild/badge/icon?subject=%20%20%20Linux-aarch64%20CI%20"/></a>
     <a href="https://github.com/eProsima/Fast-DDS/actions/workflows/nightly-windows-ci.yml"><img alt="Windows ci" src="https://github.com/eProsima/Fast-DDS/actions/workflows/nightly-windows-ci.yml/badge.svg"/></a>
     <a href="http://jenkins.eprosima.com:8080/job/nightly_fastdds_sec_master_mac"><img alt="Mac ci" src="http://jenkins.eprosima.com:8080/job/nightly_fastdds_sec_master_mac/lastCompletedBuild/badge/icon?subject=%20%20%20%20%20%20%20Mac%20CI%20"/></a>