Fixes LSAN report:
```
Direct leak of 32 byte(s) in 1 object(s) allocated from:
    #0 0x7f7448582f41 in operator new(unsigned long) /build/gcc/src/gcc/libsanitizer/asan/asan_new_delete.cpp:99
    #1 0x55676af99e7c in TestProblemStoreNode::testLabelNode() /home/milian/projects/kf5/src/extragear/kdevelop/kdevelop/kdevplatform/shell/tests/test_problemstorenode.cpp:99
```