Update errors-inbox.mdx

Adding a note about regressed errors.

src/content/docs/errors-inbox/errors-inbox.mdx

@@ -121,6 +121,10 @@ Your errors inbox displays the total number of occurrences of each error group w
 
 Using the dropdown in the top right, you can sort the list of grouped errors by the number of occurrences or by the error that was last seen (latest first).
 
+### Regression flag
+
+An error group is tagged with a regression tag when a new error matches a resolved error group’s fingerprint. The regression flag will disappear once a regressed error group's state is changed. 
+
 ### Bulk actions 
 
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