For rss2, do not mark guid as permalink, unless only link is given

[pavellishin]

When a <guid> element is given, it's considered to be an RSS feed item's permalink by default (see the spec: https://cyber.harvard.edu/rss/rss.html#ltguidgtSubelementOfLtitemgt)

This is not always the preferred behavior, since some RSS clients will treat the guid as the link when attempting to open the item in a browser, and if this is not a valid URL, this will fail. (For example, Bluesky posts' uri is not a valid URL, but instead looks like at://did:plc:abc123/app.bsky.feed.post/def456).

This PR changes the behavior to explicitly specify isPermaLink="false" if a guid or an id is given for an item, but will set it to true if only the link is given.

This addresses issue #212.

[pavellishin]

Side note: my personal preference would be for the sampleFeed to be re-generated for every test, instead of every test appending yet more items to it - otherwise, inserting a test in the middle will cause the test suite to fail because every subsequent test will be modified, and no longer match the snapshot.

I also had to make some local changes to be able to build & run tests; I have not committed those here.

[jpmonette]

@pavellishin Which changes have you had to make locally to make this work?

Thanks for the contribution.

[jpmonette]

Seems like this change broke the tests:
a0389cb

I've fixed it & added a new Github Action to run tests, this should ensure it doesn't happen again.

[pavellishin]

@pavellishin Which changes have you had to make locally to make this work?

Thanks for the contribution.

Oof, I think I cloned the repo to a temporary directory and it's gone now. I'll see if I can reproduce my issues and get back to you.

I don't have the best recollection, but some of the changes in #215 smell familiar...

[pavellishin]

Ok, I just re-cloned it, and ran pnpm i and pnpm test, and it worked fine.

I do think that's due to the changes in #215; if I check out the commit before my PR (commit:1a29418), and run pnpm test, I start getting familiar-sounding errors:

# pnpm test

> feed@5.0.1 test /Users/pavel/personal/projects/feed
> jest --silent

ReferenceError: module is not defined
    at file:///Users/pavel/personal/projects/feed/jest.config.js:1:1
    at ModuleJobSync.runSync (node:internal/modules/esm/module_job:400:35)
    at ModuleLoader.importSyncForRequire (node:internal/modules/esm/loader:427:47)
    at loadESMFromCJS (node:internal/modules/cjs/loader:1565:24)
    at Module._compile (node:internal/modules/cjs/loader:1716:5)
    at Object..js (node:internal/modules/cjs/loader:1899:10)
    at Module.load (node:internal/modules/cjs/loader:1469:32)
    at Function._load (node:internal/modules/cjs/loader:1286:12)
    at TracingChannel.traceSync (node:diagnostics_channel:322:14)
    at wrapModuleLoad (node:internal/modules/cjs/loader:235:24)
 ELIFECYCLE  Test failed. See above for more details.