fix(env_file): rename _s -> s on commit/rollback_apply to match parent

Crystal's compiler warns when an overriding method's parameter name
differs from the parent's, since named-argument callers would pass
the wrong slot. Underscore-prefix was meant as 'unused' but it changed
the parameter name, which Crystal correctly flagged.

Match the parent signature (s : Domain::NewSecret) and use the explicit
'_ = s' idiom inside the body to mark it intentionally unused. Now
'shards build cre' compiles with zero warnings.

PROJECTS/intermediate/credential-rotation-enforcer/src/cre/rotators/env_file.cr

@@ -62,14 +62,16 @@ module CRE::Rotators
       content.includes?(expected_line) && content.bytesize > 0
     end
 
-    def commit(c : Domain::Credential, _s : Domain::NewSecret) : Nil
+    def commit(c : Domain::Credential, s : Domain::NewSecret) : Nil
+      _ = s
       path = c.tag("path").not_nil!
       pending_path = "#{path}.pending"
       raise RotatorError.new("pending file missing at commit time: #{pending_path}") unless File.exists?(pending_path)
       File.rename(pending_path, path)
     end
 
-    def rollback_apply(c : Domain::Credential, _s : Domain::NewSecret) : Nil
+    def rollback_apply(c : Domain::Credential, s : Domain::NewSecret) : Nil
+      _ = s
       path = c.tag("path").not_nil!
       pending_path = "#{path}.pending"
       File.delete(pending_path) if File.exists?(pending_path)