[element model] fix prefer_final_locals

Migrates `isPotentiallyMutatedInScope2` call.


Bug: https://github.com/dart-lang/linter/issues/5099
Change-Id: I031d2133d492b42f8cb55ae0835f6de865e467d6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/391845
Auto-Submit: Phil Quitslund <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: pq

pkg/linter/lib/src/rules/prefer_final_locals.dart

@@ -55,8 +55,8 @@ class _Visitor extends SimpleAstVisitor<void> {
 
   bool isPotentiallyMutated(AstNode pattern, FunctionBody function) {
     if (pattern is DeclaredVariablePattern) {
-      var element = pattern.declaredElement;
-      if (element == null || function.isPotentiallyMutatedInScope(element)) {
+      var element = pattern.declaredElement2;
+      if (element == null || function.isPotentiallyMutatedInScope2(element)) {
         return true;
       }
     }