reverted the nominal mrtrix version to 3.0.4 in ci-cd (we are going off a branch in any case)

Author: tclose

.github/workflows/ci-cd.yaml

@@ -20,7 +20,7 @@ on:
 env:
   MRTRIX_HOME: /opt/mrtrix3
   MRTRIX_INSTALL: /opt/mrtrix3/install
-  MRTRIX_VERSION: 3.1.0a0
+  MRTRIX_VERSION: 3.0.4
   SUBPKG_NAME: v3_1
 
 jobs: