Make "SWT Matrix Tests" badge the current one

As part of working on eclipse-platform#2764
I was considering how to display badges going forward to align with
test results per platform. As it turns out the "SWT Matrix Tests"
has been stuck on an arbitrary old badge for many years now.

This PR updates it, but as it has been wrong for a long time, perhaps
removing it entirely makes more sense, but for now I update it. There
was push back in eclipse-platform#1897
against removing it.

Part of eclipse-platform#2714

Author: jonahgraham

README.md

@@ -1,6 +1,6 @@
 [![SWT Matrix Build](https://github.com/eclipse-platform/eclipse.platform.swt/actions/workflows/maven.yml/badge.svg)](https://github.com/eclipse-platform/eclipse.platform.swt/actions/workflows/maven.yml)
 [![Publish Unit Test Results](https://github.com/eclipse-platform/eclipse.platform.swt/actions/workflows/junit.yml/badge.svg)](https://github.com/eclipse-platform/eclipse.platform.swt/actions/workflows/junit.yml)
-![SWT Matrix Tests](https://gist.githubusercontent.com/eclipse-releng-bot/78d110a601baa4ef777ccb472f584038/raw/71510599eb84e852f3e135aa7a3ddf33854ca716/badge.svg)
+![SWT Matrix Tests](https://gist.githubusercontent.com/eclipse-releng-bot/78d110a601baa4ef777ccb472f584038/raw/badge.svg)
 [![License](https://img.shields.io/github/license/eclipse-platform/eclipse.platform)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/LICENSE)
 
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