NIX_IMAGE: 2.5.1 -> 2.6.0

Nix 2.6.0 has been released.
https://discourse.nixos.org/t/nix-2-6-0-released/17324

Signed-off-by: Thomas Gerbet <[email protected]>

Author: LeSuisse

bootstrap.Dockerfile

@@ -1,5 +1,5 @@
 ARG GOLANG_IMAGE=golang:1.17.5-alpine@sha256:4918412049183afe42f1ecaf8f5c2a88917c2eab153ce5ecf4bf2d55c1507b74
-ARG NIX_IMAGE=nixos/nix:2.5.1@sha256:d66c307749b460c054d8edf6191f58ec38c569c8639161d41eb6e4879baf7ff2
+ARG NIX_IMAGE=nixos/nix:2.6.0@sha256:f085a81ca39642a405b41f45e8c21a369d89c65ca9f05d3a9b78dc5852d300ff
 
 FROM ${GOLANG_IMAGE} AS build
 WORKDIR /src