Stop using deprecated AbstractDaemonTest#fail

The method is deprecated and will soon be removed. Replace it with the
new assertThrows method.

Change-Id: I8334795a041cbbc6e35ac2c5e152c1f363f9cc3c
diff --git a/src/test/java/com/googlesource/gerrit/plugins/readonly/AbstractReadOnlyTest.java b/src/test/java/com/googlesource/gerrit/plugins/readonly/AbstractReadOnlyTest.java
index e24137f..ce8d081 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/readonly/AbstractReadOnlyTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/readonly/AbstractReadOnlyTest.java
@@ -15,6 +15,7 @@
 package com.googlesource.gerrit.plugins.readonly;
 
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.gerrit.testing.GerritJUnit.assertThrows;
 import static org.apache.http.HttpStatus.SC_SERVICE_UNAVAILABLE;
 
 import com.google.gerrit.acceptance.GitUtil;
@@ -146,12 +147,9 @@
     setReadOnly(true);
 
     // Push should fail
-    try {
-      pushTo("refs/for/master");
-      fail("expected TransportException");
-    } catch (TransportException e) {
-      assertThat(e).hasMessageThat().contains("READ ONLY");
-    }
+    TransportException thrown =
+        assertThrows(TransportException.class, () -> pushTo("refs/for/master"));
+    assertThat(thrown).hasMessageThat().contains("READ ONLY");
 
     // Disable read-only
     setReadOnly(false);