Dockerfile: add execute permisson to clang-tidy-diff.py

Author: riebl

Dockerfile

@@ -55,7 +55,8 @@ COPY --from=build /omnetpp/Makefile.inc /omnetpp
 COPY --from=build /sumo-prefix/ /usr/local
 
 RUN cd /usr/local/bin && \
-    curl -sSL -O https://raw.githubusercontent.com/llvm/llvm-project/main/clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py
+    curl -sSL -O https://raw.githubusercontent.com/llvm/llvm-project/main/clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py && \
+    chmod +x clang-tidy-diff.py
 
 ENV PATH=/omnetpp/bin:$PATH
 ENV SUMO_HOME=/usr/local/share/sumo