Release process: fix terminology

We're not configuring *mirrors* in that file.

wiki/src/contribute/release_process.mdwn

@@ -1592,7 +1592,7 @@ Ask the mirrors team to disable mirrors that are lagging behind:
 
  - either over email: <tails-mirrors@boum.org>
  - or by creating a merge request that modifies the
-   [mirrors configuration file](https://gitlab.tails.boum.org/tails/mirror-pool/-/blob/master/mirrors.json)
+   [mirrors pool](https://gitlab.tails.boum.org/tails/mirror-pool/-/blob/master/mirrors.json)
 
 Sanity checks
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