Run Minconda install with bash

The Minconda installer seems to expect that `[[` can be used in all sh
implementations, which is not necessarily the case (there are some
discussions around this issue e.g. in
conda/conda#10431).

To attempt to work around this, we run the installer with bash instead.

buildscripts/incremental/install_miniconda.sh

@@ -10,4 +10,4 @@ else
   echo Error
 fi
 chmod +x miniconda.sh
-./miniconda.sh -b
+bash ./miniconda.sh