Fix the RegExp flag used for input pattern validation

According to MDN (https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/pattern#overview),
the RegExp flag was changed from 'u' to 'v' around mid-2023, so jsdom
should update to match that.

lib/jsdom/living/nodes/HTMLInputElement-impl.js

@@ -1025,8 +1025,8 @@ class HTMLInputElementImpl extends HTMLElementImpl {
             // The pattern attribute should be matched against the entire value, not just any
             // subset, so add ^ and $ anchors. But also check the validity of the regex itself
             // first.
-            new RegExp(pattern, "u"); // eslint-disable-line no-new
-            regExp = new RegExp("^(?:" + pattern + ")$", "u");
+            new RegExp(pattern, "v"); // eslint-disable-line no-new
+            regExp = new RegExp("^(?:" + pattern + ")$", "v");
           } catch (e) {
             return false;
           }