nixpkgs-check-by-name/scripts: Use local Nixpkgs for dependencies

Especially needed because NIX_PATH is set to something custom in the
nix-shell of nixpkgs-check-by-name

pkgs/test/nixpkgs-check-by-name/scripts/run-local.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i bash -p jq
+#!nix-shell -i bash -p jq -I nixpkgs=../../../..
 
 set -o pipefail -o errexit -o nounset
 

pkgs/test/nixpkgs-check-by-name/scripts/update-pinned-tool.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i bash -p jq
+#!nix-shell -i bash -p jq -I nixpkgs=../../../..
 
 set -o pipefail -o errexit -o nounset