Merge branch 'fix_dp3_version' into 'master'

Fix DP3 version. I think the new version breaks because it expects c++ >= 20

See merge request !24

docker/Dockerfile

@@ -86,7 +86,7 @@ RUN git clone --no-checkout \
     cmake .. && \
     make install -j`nproc`
 
-ARG DP3_COMMIT=master
+ARG DP3_COMMIT=86fba922
 RUN git clone --no-checkout \
         https://git.astron.nl/RD/DP3.git && \
     mkdir DP3/build && \