change git URL

reg-app/Dockerfile

 FROM alpine/git AS clone
 WORKDIR /app
-RUN git clone https://git.scc.kit.edu/simon/reg-app.git
+RUN git clone https://git.scc.kit.edu/reg-app/reg-app.git
 WORKDIR /app/reg-app
 RUN git checkout tags/2.7.5 -b branch-2.7.5