Run rubocop 1.77.0 on tree (#12097)

.pre-commit-config.yaml

@@ -3,7 +3,7 @@
 # These pre-commit hooks mirror the Github CI, so running them locally will catch errors earlier.
 repos:
   - repo: https://github.com/rubocop/rubocop
-    rev: v1.76.0
+    rev: v1.77.0
     hooks:
       - id: rubocop
   - repo: https://github.com/syntaqx/git-hooks

lib/gem_compact_index_client.rb

@@ -31,6 +31,6 @@ class BasicCompactIndexClient
     return [] if data.nil? || data.empty?
     lines = data.split("\n")
     header = lines.index('---')
-    header ? lines[header + 1..] : lines
+    header ? lines[(header + 1)..] : lines
   end
 end