Build fails trying to install isl

[ArchKudo]

I downloaded the v009 binary, and ran

 nix-portable nix-shell -p bash

but it fails with the following error:

warning: error: unable to download 'http://isl.gforge.inria.fr/isl-0.17.1.tar.xz': Timeout was reached (28); retrying in 274 ms
warning: error: unable to download 'http://isl.gforge.inria.fr/isl-0.17.1.tar.xz': Timeout was reached (28); retrying in 612 ms
warning: error: unable to download 'http://isl.gforge.inria.fr/isl-0.17.1.tar.xz': Timeout was reached (28); retrying in 1170 ms
^[[B^[[Bwarning: error: unable to download 'http://isl.gforge.inria.fr/isl-0.17.1.tar.xz': Timeout was reached (28); retrying in 2150 ms
error: unable to download 'http://isl.gforge.inria.fr/isl-0.17.1.tar.xz': Timeout was reached (28)
error: builder for '/nix/store/g2ag62lgniwh7gisv3qk721l93wrhm71-isl-0.17.1.tar.xz.drv' failed with exit code 1
error: 1 dependencies of derivation '/nix/store/mq3nnxd4rznimdjv51czdmpnzklj9zm8-isl-0.17.1.drv' failed to build
error: 1 dependencies of derivation '/nix/store/ll8mjfvnhd3rq0vf56qrxqxa0iqvb8i1-gcc-9.3.0.drv' failed to build
building '/nix/store/vd1qyrzvbchgflbgrf3y588k5af0d7mj-libffi-3.3.tar.gz.drv'...
error: 1 dependencies of derivation '/nix/store/hxa00450r312f19vhsx9d9z2k5f8dlfi-bootstrap-stage4-gcc-wrapper-9.3.0.drv' failed to build
error: 1 dependencies of derivation '/nix/store/bmk3hs8m6wcnvk9cg30z3fhjkdhfbxgn-stdenv-linux.drv' failed to build
error: 1 dependencies of derivation '/nix/store/7vjnd11idy69hhnrnj2yzjy1hri9h0yc-test.drv' failed to build
+ echo 'Fatal error: nix is unable to build packages'
Fatal error: nix is unable to build packages
+ exit 1

According to this pr there is a new mirror available, but unsure how to change that, any guidance on how to fix this? thanks!

System Information

$ uname -a
Linux xxx.ac.uk 5.10.0-21-amd64 #1 SMP Debian 5.10.162-1 (2023-01-21) x86_64 GNU/Linux