test: use canonical nested library imports

lib/ww/syntax/ast_test.ww

@@ -7,7 +7,7 @@
 
 package syntax_test;
 
-import syntax;
+import ww.syntax;
 
 
 fn checknkname(k: nkind, want: str) void = {

lib/ww/syntax/sym_test.ww

@@ -9,7 +9,7 @@
 
 package syntax_test;
 
-import syntax;
+import ww.syntax;
 
 @test fn scope_define_lookup() void = {
 	let s: *scope = newscope(nil);

lib/ww/syntax/tok_test.ww

@@ -19,7 +19,7 @@
 package syntax_test;
 
 import os;
-import syntax;
+import ww.syntax;
 import temp;