fix(easy-typography): incorporates changes from community

Incoroporates changes from [this
PR](https://github.com/typst/packages/pull/1527) and updates tests
accordingly.

Thank you to [neuralpain](https://github.com/neuralpain) and
[ssotoen](https://github.com/ssotoen) for the suggestions and code
fixes.

easy-typography/tests/basic/test.typ

@@ -6,7 +6,7 @@
 #codly(languages: codly-languages)
 
 #show: easy-typography.with(
-  fonts: (heading: "Source Sans Pro", body: "Source Serif Pro"),
+  fonts: (heading: "Source Sans 3", body: "Source Serif 4"),
 )
 
 = Introducing Easy Typography