Add step to manually clean workspace. (#334)

Co-authored-by: valandil <valandil211@proton.me>

Jenkinsfile

@@ -71,4 +71,10 @@ pipeline {
     QEMU_IRIX = credentials('qemu-irix')
     ROMS_DIR = credentials('roms')
   }
+
+  post {
+    always {
+      cleanWs()
+    }
+  }
 }