[lldb] Further constrain a test that fails without python enabled

The test relies on the python embedded interpreter being available and
fails otherwise.

lldb/test/Shell/SymbolFile/DWARF/split-optimized.c

@@ -3,6 +3,9 @@
 // -gsplit-dwarf is supported only on Linux.
 // REQUIRES: system-linux
 
+// This test uses lldb's embedded python interpreter
+// REQUIRES: python
+
 // ObjectFileELF::ApplyRelocations does not implement arm32.
 // XFAIL: target-arm && linux-gnu