Revert "use f-strings when building 'pattern'"

revert d7c97d5a97.

gallery_dl/extractor/bbc.py

@@ -21,7 +21,7 @@ class BbcGalleryExtractor(GalleryExtractor):
     directory_fmt = ("{category}", "{path:I}")
     filename_fmt = "{num:>02}.{extension}"
     archive_fmt = "{programme}_{num}"
-    pattern = rf"{BASE_PATTERN}[^/?#]+(?!/galleries)(?:/[^/?#]+)?)$"
+    pattern = BASE_PATTERN + r"[^/?#]+(?!/galleries)(?:/[^/?#]+)?)$"
     example = "https://www.bbc.co.uk/programmes/PATH"
 
     def metadata(self, page):
@@ -71,7 +71,7 @@ class BbcProgrammeExtractor(Extractor):
     category = "bbc"
     subcategory = "programme"
     root = "https://www.bbc.co.uk"
-    pattern = rf"{BASE_PATTERN}[^/?#]+/galleries)(?:/?\?page=(\d+))?"
+    pattern = BASE_PATTERN + r"[^/?#]+/galleries)(?:/?\?page=(\d+))?"
     example = "https://www.bbc.co.uk/programmes/ID/galleries"
 
     def items(self):