fix(linkedin): add fallback for date parsing on new job listings (#343)

LinkedIn uses two CSS classes for job posting dates:
- `job-search-card__listdate` for older posts
- `job-search-card__listdate--new` for recent posts (< 24h)

The scraper only checked the first class, causing `date_posted` to be
None for all fresh listings. This adds a fallback to also check for
the `--new` variant.

jobspy/linkedin/__init__.py

@@ -209,6 +209,10 @@ class LinkedIn(Scraper):
             if metadata_card
             else None
         )
+        if not datetime_tag and metadata_card:
+            datetime_tag = metadata_card.find(
+                "time", class_="job-search-card__listdate--new"
+            )
         date_posted = None
         if datetime_tag and "datetime" in datetime_tag.attrs:
             datetime_str = datetime_tag["datetime"]