Fix Sass compilation in tests

There is a bug where `sass.compile` will throw with an extremely
unhelpful error trace when running in Jest [[1]].

>     TypeError: J.getInterceptor$ax(...).map$1$1 is not a function
>
>     at Object.map$1$1$ax (node_modules/sass/sass.dart.js:24513:44)
>     at listDir_closure0.call$0 (node_modules/sass/sass.dart.js:87066:18)
>     at Object._systemErrorToFileSystemException0 (node_modules/sass/sass.dart.js:20776:23)
>     at Object.listDir0 (node_modules/sass/sass.dart.js:20771:16)
>     at _realCasePath_helper_closure0.call$0 (node_modules/sass/sass.dart.js:84710:34)
>     at JsLinkedHashMap.putIfAbsent$2 (node_modules/sass/sass.dart.js:27273:24)
>     at _realCasePath_helper0.call$1 (node_modules/sass/sass.dart.js:84699:32)
>     at _realCasePath_helper_closure0.call$0 (node_modules/sass/sass.dart.js:84706:35)
>     at JsLinkedHashMap.putIfAbsent$2 (node_modules/sass/sass.dart.js:27273:24)
>     at _realCasePath_helper0.call$1 (node_modules/sass/sass.dart.js:84699:32)

It has been suggested
that it is related to `path.absolute` being overridden by the jsdom
environment [[2]], but the workaround of using the "node" environment
does not solve the issue for us.

Instead, what did work is using the legacy API [[3]]. I'm not sure why
this is, but it seems to do the trick. Note that with the legacy API,
the file path is part of the options object, rather than being the
first argument. If you forget to change the call signature, you will get
a different unhelpful error message:

> NoSuchMethodError: method not found: 'call'

[1]: sass/dart-sass#1692
[2]: sass/dart-sass#710 (comment)
[3]: https://sass-lang.com/documentation/js-api#legacy-api

run-tasks.js

@@ -43,7 +43,8 @@ function sass () {
   fs.readdirSync('app/assets/sass').forEach(file => {
     if (!file.endsWith('.scss')) return
 
-    const result = sass.compile('app/assets/sass/' + file, {
+    const result = sass.renderSync({
+      file: 'app/assets/sass/' + file,
       logger: sass.Logger.silent,
       loadPaths: [__dirname],
       sourceMap: true,