[knx] Fix warnings in test (openhab#16434)

Signed-off-by: Holger Friedrich <[email protected]>

Author: holgerfriedrich

bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/channel/KNXChannelTest.java

@@ -197,7 +197,7 @@ void test5001PercentType() throws KNXFormatException {
         Command command = new PercentType("90");
         @Nullable
         OutboundSpec outboundSpec = knxChannel.getCommandSpec(command);
-        assertThat(outboundSpec, is(notNullValue()));
+        assertNotNull(outboundSpec);
         assertThat(outboundSpec.getGroupAddress(), is(new GroupAddress("1/2/2")));
 
         String mappedValue = ValueEncoder.encode(outboundSpec.getValue(), outboundSpec.getDPT());
@@ -217,8 +217,9 @@ void test1001ToDimmerChannel() throws KNXFormatException {
         assertThat(knxChannel, instanceOf(TypeDimmer.class));
 
         Command command = OnOffType.ON;
+        @Nullable
         OutboundSpec outboundSpec = knxChannel.getCommandSpec(command);
-        assertThat(outboundSpec, is(notNullValue()));
+        assertNotNull(outboundSpec);
         assertThat(outboundSpec.getGroupAddress(), is(new GroupAddress("1/2/1")));
 
         String mappedValue = ValueEncoder.encode(outboundSpec.getValue(), outboundSpec.getDPT());