Plugins script: Apply 'black' formatting left-over

Do so as prescribed under [1]'s script code formatting instructions.

[1] https://www.gerritcodereview.com/publishing.html#updating-the-plugins-page

Change-Id: Ib973c2d21c8987c89c58baaf53a2ee3502b4edd4
diff --git a/tools/plugins.py b/tools/plugins.py
index 99058a2..1b1fefe 100644
--- a/tools/plugins.py
+++ b/tools/plugins.py
@@ -16,7 +16,9 @@
 from tqdm import tqdm
 
 
-BRANCHES = ["master"] + [f"stable-{version}" for version in ["3.2", "3.1", "3.0", "2.16"]]
+BRANCHES = ["master"] + [
+    f"stable-{version}" for version in ["3.2", "3.1", "3.0", "2.16"]
+]
 CI = "https://gerrit-ci.gerritforge.com"
 GERRIT = "https://gerrit-review.googlesource.com"
 GITILES = "https://gerrit.googlesource.com"