Fix regression in #20608. (#20745)

src/Microsoft.PowerShell.Commands.Utility/commands/utility/Group-Object.cs

@@ -153,7 +153,7 @@ namespace Microsoft.PowerShell.Commands
 
                         foreach (object item in propertyValueItems)
                         {
-                            sb.AppendFormat(CultureInfo.CurrentCulture, $"{item}, ");
+                            sb.Append(CultureInfo.CurrentCulture, $"{item}, ");
                         }
 
                         sb = sb.Length > length ? sb.Remove(sb.Length - 2, 2) : sb;
@@ -161,7 +161,7 @@ namespace Microsoft.PowerShell.Commands
                     }
                     else
                     {
-                        sb.AppendFormat(CultureInfo.CurrentCulture, $"{propValuePropertyValue}, ");
+                        sb.Append(CultureInfo.CurrentCulture, $"{propValuePropertyValue}, ");
                     }
                 }
             }

test/powershell/Modules/Microsoft.PowerShell.Utility/Group-Object.Tests.ps1

@@ -130,6 +130,14 @@ Describe "Group-Object" -Tags "CI" {
         $result[0].Name | Should -Be ""
         $result[0].Group | Should -Be '@{X=}'
     }
+
+    It "Should handle format-like strings with curly braces like normal strings" {
+        $result = '{', '}', '{0}' | Group-Object
+        $result.Count | Should -Be 3
+        $result[0].Name | Should -BeExactly '{'
+        $result[1].Name | Should -BeExactly '{0}'
+        $result[2].Name | Should -BeExactly '}'
+    }
 }
 
 Describe "Check 'Culture' parameter in order object cmdlets (Group-Object, Sort-Object, Compare-Object)" -Tags "CI" {