[SECURITY][Bugfix:TAGrading] Prevent loading of SVG+XML files (#6646)
[SECURITY][Bugfix:TAGrading] Prevent loading of SVG+XML files (#6646)

Co-authored-by: Chris Reed <aab780deaa45ed0af851c804a13faef6b70737e7@users.noreply.github.com>
Submitty/Submitty,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,Submitty/Submitty,Submitty/Submitty,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,Submitty/Submitty,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,Submitty/Submitty,Submitty/Submitty,Submitty/Submitty,Submitty/Submitty,RCOS-Grading-Server/HWserver,Submitty/Submitty