klogr: simplify test failure message

The mismatch is easier to see when the output is printed above
each other instead of side-by-side.

klogr/klogr_test.go

@@ -200,7 +200,7 @@ func testOutput(t *testing.T, format string) {
 				expectedOutput = test.expectedKlogOutput
 			}
 			if actual != expectedOutput {
-				t.Errorf("expected %q did not match actual %q", expectedOutput, actual)
+				t.Errorf("Expected:\n%s\nActual:\n%s\n", expectedOutput, actual)
 			}
 		})
 	}

ktesting/testinglogger_test.go

@@ -118,7 +118,7 @@ func TestInfo(t *testing.T) {
 
 			actual := buffer.String()
 			if actual != test.expectedOutput {
-				t.Errorf("expected %q did not match actual %q", test.expectedOutput, actual)
+				t.Errorf("Expected:\n%sActual:\n%s\n", test.expectedOutput, actual)
 			}
 		})
 	}