6.3.0.4: SdImportTest::testDocumentLayout fails

Dear LibreOffice folks,


Building LibreOffice 6.3.0.4 with `DISPLAY=` (unset) the test below fails.

```
bootstrapfixture.cxx:199:Assertion
Test name: SdImportTest::testDocumentLayout
equality assertion failed
- Expected: 0
- Actual  : 256
- failed to execute: sh
/dev/shm/bee-root/libreoffice/libreoffice-6.3.0.4-0/build/bin/odfvalidator.sh
-M
/dev/shm/bee-root/libreoffice/libreoffice-6.3.0.4-0/source/schema/libreoffice/OpenDocument-manifest-schema-v1.3+libreoffice.rng
-D
/dev/shm/bee-root/libreoffice/libreoffice-6.3.0.4-0/source/schema/libreoffice/OpenDocument-dsig-schema-v1.3+libreoffice.rng
-O
/dev/shm/bee-root/libreoffice/libreoffice-6.3.0.4-0/source/schema/libreoffice/OpenDocument-schema-v1.3+libreoffice.rng
-m
/dev/shm/bee-root/libreoffice/libreoffice-6.3.0.4-0/source/schema/mathml2/mathml2.xsd
/tmp/lu933312w9ae3.tmp > /tmp/lu933312w9ae8.tmp

Failures !!!
Run: 84   Failure total: 1   Failures: 1   Errors: 0

Error: a unit test failed, please do one of:

make CppunitTest_sd_import_tests CPPUNITTRACE="gdb --args"
    # for interactive debugging on Linux
make CppunitTest_sd_import_tests VALGRIND=memcheck
    # for memory checking
make CppunitTest_sd_import_tests DEBUGCPPUNIT=TRUE
    # for exception catching

You can limit the execution to just one particular test by:

make CPPUNIT_TEST_NAME="testXYZ" ...above mentioned params...

make[1]: ***
[/dev/shm/bee-root/libreoffice/libreoffice-6.3.0.4-0/source/solenv/gbuild/CppunitTest.mk:113:
/dev/shm/bee-root/libreoffice/libreoffice-6.3.0.4-0/build/workdir/CppunitTest/sd_import_tests.test]
Error 1
```

Kind regards,

Paul