Add .tofu/.tofutest.hcl to tofu fmt error message. (#3947)

Signed-off-by: Andy Brody <git@abrody.com>

internal/command/fmt.go

@@ -160,7 +160,7 @@ func (c *FmtCommand) fmt(paths []string, stdin io.Reader, stdout io.Writer, args
 			}
 
 			if !fmtd {
-				diags = diags.Append(fmt.Errorf("Only .tf, .tfvars, and .tftest.hcl files can be processed with tofu fmt"))
+				diags = diags.Append(fmt.Errorf("Only .tf, .tofu, .tfvars, .tftest.hcl, and .tofutest.hcl files can be processed with tofu fmt"))
 				continue
 			}
 		}