Update base image tag in tools.Dockerfile to base.master.78b9a056.20260421.1

[ComradeCow]

Summary

Update the base image tag in \linux/tools.Dockerfile\ as part of the steady_osprey base image release.

Change Required

In \linux/tools.Dockerfile, update the \ARG IMAGE_LOCATION\ line:

From:
\
ARG IMAGE_LOCATION=cloudconregprd.azurecr.io/public/azure-cloudshell:base.master.13613232.20260406.1
\\

To:
\
ARG IMAGE_LOCATION=cloudconregprd.azurecr.io/public/azure-cloudshell:base.master.78b9a056.20260421.1
\\

This is the only change needed. No other files should be modified.