Add missing prefix for CheckoutSessionItemId

[eric-seppanen]

Summary

Adds the missing "li_" prefix for CheckoutSessionItemId.

This can be seen in the documentation here: https://stripe.com/docs/api/checkout/sessions/line_items

I also see the same prefix with the Stripe CLI, using stripe checkout sessions list --expand data.line_items

Checklist

• [x] ran cargo make fmt
• [x] using conventional commits to hightlight user-facing fixes and features

[eric-seppanen]

I also verified the modified crate against data from a live stripe API:

let expand = ["line_items"];
let result = CheckoutSession::retrieve(&client, &session_id, &expand).await?;
println!("{result:#?}");

and observed within the results:

   line_items: List {
        data: [
            CheckoutSessionItem {
                id: CheckoutSessionItemId(
                    "li_1Mh3pWFf8peiXbpDMszIA8TT",
                ),
...

[arlyon]

Solid, TY. Going to run CI and merge.

[codecov[bot]]

Codecov Report

Merging #349 (c6bdb57) into master (8643cb3) will increase coverage by 0.01%. The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #349      +/-   ##
=========================================
+ Coverage    6.41%   6.42%   +0.01%     
=========================================
  Files         131     131              
  Lines       20546   20546              
=========================================
+ Hits         1317    1320       +3     
+ Misses      19229   19226       -3     

Impacted Files	Coverage Δ
src/ids.rs	56.33% <ø> (ø)
src/resources/generated/subscription.rs	1.50% <0.00%> (+0.32%)	:arrow_up:

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