fix(cloud): synced reviewers should be unique (#1377)

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## What this PR does / why we need it:

Before, if the same user did multiple reviews, the synced reviewer list
would contain duplicates. This PR changes it so that each reviewer is
only included once.

## Which issue(s) this PR fixes:
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## Does this PR introduce a user-facing change?
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no
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cmd/terramate/cli/cloud.go

@@ -435,9 +435,18 @@ func (c *cli) detectCloudMetadata() {
 				Msg("failed to retrieve PR reviews")
 		}
 
+		uniqueReviewers := make(map[string]struct{})
+
 		for _, review := range reviews {
+			login := review.User.Login
+
+			if _, found := uniqueReviewers[login]; found {
+				continue
+			}
+			uniqueReviewers[login] = struct{}{}
+
 			reviewRequest.Reviewers = append(reviewRequest.Reviewers, cloud.Reviewer{
-				Login:     review.User.Login,
+				Login:     login,
 				AvatarURL: review.User.AvatarURL,
 			})
 		}