samples: drivers/entropy yaml regex fix

The last regex in the yaml file did not match when executing the test on
an embedded target. The expected two spaces are not present at the
beginning of the line.

Fixes zephyrproject-rtos#23919

Signed-off-by: Christian Taedcke <christian.taedcke@lemonbeat.com>

samples/drivers/entropy/sample.yaml

@@ -11,4 +11,4 @@ tests:
       regex:
         - "Entropy Example! (.*)"
         - "entropy device is (.*), name is (.*)"
-        - "(  0x([0-9a-f]){2}){9}"
+        - "(\\s*0x([0-9a-f]){2}){9}"