[DebugInfo] Adjusting DWARF version to fix a test failure in aix-ppc64 pipeline (llvm#167019)

Test added in llvm#165023 had DWARF V5 but for the targets that uses
`XCOFF`, some sections of DWARF v5 are not initialized.

Author: laxmansole

llvm/test/DebugInfo/extradata-node-reference.ll

@@ -29,7 +29,7 @@
 !1 = !DIFile(filename: "test.cpp", directory: ".")
 !2 = !{i32 2, !"Debug Info Version", i32 3}
 !3 = !{i32 1, !"wchar_size", i32 4}
-!4 = !{i32 2, !"Dwarf Version", i32 5}
+!4 = !{i32 2, !"Dwarf Version", i32 4}
 !8 = !{!9, !16, !24, !35}
 
 ; extraData node definitions