fix: avoid test Docker crash

This avoids the following error that appeared in Jenkins

tests.Dockerfile:17
--------------------
  15 |         && rm -rf /var/lib/apt/lists/*
  16 |
  17 | >>> RUN ln -s /usr/bin/python3 /usr/bin/python
  18 |
  19 |     RUN mkdir -p /etc/apt/keyrings && \
--------------------
ERROR: failed to build: failed to solve: process "/bin/sh -c ln -s
/usr/bin/python3 /usr/bin/python" did not complete successfully: exit
code: 1
[Pipeline] }

Author: Ivansete-status

_assets/ci/tests.Dockerfile

@@ -14,7 +14,7 @@ RUN apt-get update && apt-get install -yq --no-install-recommends --fix-missing
     openssh-client \
     && rm -rf /var/lib/apt/lists/*
 
-RUN ln -s /usr/bin/python3 /usr/bin/python
+RUN ln -sf /usr/bin/python3 /usr/bin/python
 
 RUN mkdir -p /etc/apt/keyrings && \
     curl -fsSL https://download.docker.com/linux/debian/gpg  | gpg --dearmor -o /etc/apt/keyrings/docker.gpg && \