Update env to set KOIOS_API for sanchonet (#1806)

## Description
Sets KOIOS_API varaible.

## Motivation and context
KOIOS has an API for sanchonet (sancho) it is just not being set in the
case statements.

## Which issue it fixes?
Closes #1805

scripts/cnode-helper-scripts/env

@@ -1194,7 +1194,8 @@ case ${NWMAGIC} in
     [[ -z ${KOIOS_API} ]] && KOIOS_API="https://preview.koios.rest/api/v1";;
   4)
     NETWORK_NAME="Sanchonet"
-    SHELLEY_TRANS_EPOCH=0;;
+    SHELLEY_TRANS_EPOCH=0
+    [[ -z ${KOIOS_API} ]] && KOIOS_API="https://sancho.koios.rest/api/v1";;
   *) 
     NETWORK_NAME="Custom"
     [[ -z ${SHELLEY_TRANS_EPOCH} ]] && SHELLEY_TRANS_EPOCH=0