dashboard/app: change regressions email title

Closes #6380.

Author: tarasmadan

dashboard/app/reporting_email.go

@@ -181,7 +181,7 @@ func sendNsCoverageReport(ctx context.Context, ns, email string,
 			coveragePageLink(ns, period[1].Type, period[1].DateTo.String(), minDrop, 2, true)),
 		Table: table,
 	}
-	title := fmt.Sprintf("%s coverage regression (%s)->(%s)", ns, periodFrom, periodTo)
+	title := fmt.Sprintf("%s coverage regression in %s", ns, periodTo)
 	err = sendMailTemplate(ctx, &mailSendParams{
 		templateName: "mail_ns_coverage.txt",
 		templateArg:  args,

dashboard/app/reporting_test.go

@@ -1406,7 +1406,7 @@ func TestCoverageRegression(t *testing.T) {
 	assert.Equal(t, 1, len(c.emailSink))
 	msg := <-c.emailSink
 	assert.Equal(t, []string{"[email protected]"}, msg.To)
-	assert.Equal(t, "coverage-tests coverage regression (November 1999)->(December 1999)", msg.Subject)
+	assert.Equal(t, "coverage-tests coverage regression in December 1999", msg.Subject)
 	wantLink := "https://testapp.appspot.com/coverage-tests/coverage?" +
 		"dateto=1999-12-31&min-cover-lines-drop=1&order-by-cover-lines-drop=1&period=month&period_count=2"
 	assert.Equal(t, `Regressions happened in 'coverage-tests' from November 1999 (30 days) to December 1999 (31 days).