Update error message in _zoneinfo.py to use f-string (GH-20577)


Inline with the rest of the file, updated error message to use f-string.
(cherry picked from commit 5b9fbbabacca0378755fd9cadc4a7cc01a71eaef)

Co-authored-by: aboddie <64019758+aboddie@users.noreply.github.com>
diff --git a/Lib/zoneinfo/_zoneinfo.py b/Lib/zoneinfo/_zoneinfo.py
index 7b1718a..9810637 100644
--- a/Lib/zoneinfo/_zoneinfo.py
+++ b/Lib/zoneinfo/_zoneinfo.py
@@ -742,7 +742,7 @@
 
     if not -86400 < total < 86400:
         raise ValueError(
-            "Offset must be strictly between -24h and +24h:" + tz_delta
+            f"Offset must be strictly between -24h and +24h: {tz_delta}"
         )
 
     # Yes, +5 maps to an offset of -5h