Add: Mageia 9 (#52)

Author: n-thumann

.github/workflows/build.yml

@@ -90,6 +90,8 @@ jobs:
             TAG: "7"
           - CONTEXT: operating_systems/mageia
             TAG: "8"
+          - CONTEXT: operating_systems/mageia
+            TAG: "9"
           - CONTEXT: operating_systems/oraclelinux
             TAG: "5"
             UPDATED: false

README.md

@@ -59,6 +59,7 @@ When done, the container can be stopped with `docker stop target`.
 - [Mageia](https://ghcr.io/greenbone/vt-test-environments/mageia) (`mageia`)
     - `7`
     - `8`
+    - `9`
 - [Oracle Linux](https://ghcr.io/greenbone/vt-test-environments/oraclelinux) (`oraclelinux`)
     - `5`
     - `6`