Add back RHEL 8.6 configuration for Qt Creator builds

Qt Creator uses Rhel8.6 from 6.6 branch in builds, bring back the
configuration.

Change-Id: Id0f51c4eb770404cc5fc18e372d6ff861a5e99cb
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

coin/platform_configs/qt-creator.yaml

@@ -15,6 +15,12 @@ Configurations:
     Configure arguments: ''
     Environment variables: []
     Environment script: ['%ProgramFiles%\Microsoft Visual Studio\2019\Professional\VC\Auxiliary\Build\vcvarsall.bat', 'x86']
+-
+    Template: 'qtci-linux-RHEL-8.6-x86_64-50'
+    Compiler: 'GCC'
+    Features: ['Packaging', 'Sccache', 'DebugAndRelease']
+    Configure arguments: ''
+    Environment variables: []
 -
     Template: 'qtci-linux-RHEL-8.8-x86_64-50'
     Compiler: 'GCC'