community[patch]: bugfix for YoutubeLoader's LINES format (#22815)

- **Description:** A change I submitted recently introduced a bug in
`YoutubeLoader`'s `LINES` output format. In those conditions, curly
braces ("`{}`") creates a set, not a dictionary. This bugfix explicitly
specifies that a dictionary is created.
- **Issue:** N/A
- **Dependencies:** N/A
- **Twitter:** lsloan_umich
- **Mastodon:**
[lsloan@mastodon.social](https://mastodon.social/@lsloan)

libs/community/langchain_community/document_loaders/youtube.py

@@ -282,11 +282,11 @@ class YoutubeLoader(BaseLoader):
                 map(
                     lambda transcript_piece: Document(
                         page_content=transcript_piece["text"].strip(" "),
-                        metadata={
+                        metadata=dict(
                             filter(
                                 lambda item: item[0] != "text", transcript_piece.items()
                             )
-                        },
+                        ),
                     ),
                     transcript_pieces,
                 )