perf: Remove redundant Contains check in SecretObfuscator

The Contains check was redundant because StringBuilder.Replace already
handles the case where the search string doesn't exist. Additionally,
the check was done on the original input string while Replace operates
on the StringBuilder, creating an inconsistency after the first
replacement.

Fixes #1549

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: thomhurst

src/ModularPipelines/Engine/SecretObfuscator.cs

@@ -29,10 +29,7 @@ public string Obfuscate(string? input, object? optionsObject)
 
         foreach (var secret in _secretProvider.Secrets.Concat(secretsFromExtraObject))
         {
-            if (input.Contains(secret))
-            {
-                stringBuilder.Replace(secret, LoggingConstants.SecretMask);
-            }
+            stringBuilder.Replace(secret, LoggingConstants.SecretMask);
         }
 
         return stringBuilder.ToString();