Disable no-non-null assertions lint rule (#22348)

This *allows* us to use `variable!.prop` to ensure `variable` is not null/undefined.

.eslintrc.js

@@ -30,6 +30,8 @@ module.exports = {
 
             // We disable this while we're transitioning
             "@typescript-eslint/no-explicit-any": "off",
+            // We're okay with assertion errors when we ask for them
+            "@typescript-eslint/no-non-null-assertion": "off",
 
             // Ban matrix-js-sdk/src imports in favour of matrix-js-sdk/src/matrix imports to prevent unleashing hell.
             "no-restricted-imports": ["error", {