CLDR-18209 spec: fix broken link to modifications section (unicode-org#5090)

Author: srl295

docs/ldml/tr35.md

@@ -4300,7 +4300,7 @@ This section is now in a separate part, [Acknowledgments](tr35-acknowledgments.m
 
 ## Modifications
 
-This section is now in a separate part, [Modifications](tr35-modifications#modifications)
+This section is now in a separate part, [Modifications](tr35-modifications.md#modifications)
 
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