v2.6 stokes example does not build out of the box

Hi everyone,

when checking out dune-functions releases/2.6 and using dunecontrol to build it (and the required dune dependencies ofc) a compilation error occurs in the Stokes example.

Steps to reproduce:

# Start with a clean directory and get all the dune-functions dependencies and dune-functions source:
git clone https://gitlab.dune-project.org/core/dune-common.git
git clone https://gitlab.dune-project.org/core/dune-geometry.git
git clone https://gitlab.dune-project.org/core/dune-grid.git
git clone https://gitlab.dune-project.org/core/dune-istl.git
git clone https://gitlab.dune-project.org/core/dune-localfunctions.git
git clone https://gitlab.dune-project.org/staging/dune-typetree.git
git clone https://gitlab.dune-project.org/staging/dune-functions.git
# checkout release 2.6.0
for d in ./dune-*/ ; do
    cd $d
    git checkout v2.6.0 -b r2.6
    cd ..
done
# build dune-functions
dune-common/bin/dunecontrol all &> build.log &

I've attached the output from the build process. build.log

Other details:
g++ v10.3.0
cmake v3.18.4 OS: PopOS 21.04 (Basically Ubuntu 21.04 for all practical purposes)
Kernel: Linux 5.13.0-7614-generic x86_64

Do you need any other information or can I fix this locally on my end?