fix(language-service): avoid interpolation highlighting inside @let

This change omits treating `{{ }}` interpolation syntax as valid inside `@let` binding strings, preventing the interpolation curly braces from superseding the match of the surrounding binding expression and ensuring the highlighter reflects the correct semantics of `@let` bindings.

fixes #61643

(cherry picked from commit 9f5744a92d)

vscode-ng-language-service/syntaxes/src/template.ts

@@ -10,7 +10,7 @@ import {GrammarDefinition} from './types';
 
 export const Template: GrammarDefinition = {
   scopeName: 'template.ng',
-  injectionSelector: 'L:text.html -comment -control.block.ng',
+  injectionSelector: 'L:text.html -comment -control.block.ng -meta.definition.variable.ng',
   patterns: [{include: '#interpolation'}],
   repository: {
     interpolation: {

vscode-ng-language-service/syntaxes/template.json

@@ -1,6 +1,6 @@
 {
   "scopeName": "template.ng",
-  "injectionSelector": "L:text.html -comment -control.block.ng",
+  "injectionSelector": "L:text.html -comment -control.block.ng -meta.definition.variable.ng",
   "patterns": [
     {
       "include": "#interpolation"