fix(build): disable problematic marktree assert in RelWithDebInfo builds

Workaround (not a fix) for #27196 and for #33067

Asserts are meant to apply to debug builds but not release
builds for users. However the intermediate RelWithDebInfo
build type is quite often used by end users, so we might
want to disable certain problematic asserts there, while
still preserving them in Debug mode for CI.

src/nvim/marktree.c

@@ -372,7 +372,13 @@ static void unintersect_node(MarkTree *b, MTNode *x, uint64_t id, bool strict)
     }
   }
   if (strict) {
+#ifndef RELDEBUG
+    // TODO(bfredl): This assert has been seen to fail for end users
+    // using RelWithDebInfo builds. While indicating an invalid state for
+    // the marktree, this error doesn't need to be fatal. The assert still
+    // needs to present in Debug builds to be able to detect regressions in tests.
     assert(seen);
+#endif
   }
 
   if (seen) {