fix: eslint DeprecationWarning #5287

    (node:99880) DeprecationWarning: "no-incorrect-once-usage" rule is
    using `context.getScope()`, which is deprecated and will be removed
    in ESLint v9. Please use `sourceCode.getScope()` instead. (Use `node
    --trace-deprecation ...` to show where the warning was created)

Notes:
Consider:
```
L1: const x = 1
L2: const y = 2, z = 3
```
There are two `VariableDeclaration` here (L1, L2). L1 node.declarations is `[x=1]`. L2 node.declarations is `[y=2, z=3]`.

Whether you take the root node level (L1/L2) or the individual declarations in each root, the scope is the same.

Author: justinmk3

plugins/eslint-plugin-aws-toolkits/lib/rules/no-incorrect-once-usage.ts

@@ -122,7 +122,7 @@ export default ESLintUtils.RuleCreator.withoutDocs({
                         declaration.init.callee?.type === AST_NODE_TYPES.Identifier &&
                         declaration.init.callee.name === 'once'
                     ) {
-                        const scope = context.getScope()
+                        const scope = context.sourceCode.getScope(declaration)
                         const variable = scope.variables.find(
                             v => v.name === (declaration.id as TSESTree.Identifier).name
                         ) // we already confirmed the type in the if statement... why is TS mad?