Increase baud rate of mbed-os-example-crash-reporting to 115200

At 9600 baud, a large part of the serial output of the crash reporting
example is missing on CI boards, causing the example test to fail. At
a higher serial speed (115200 baud), the entire output is intact.

This is in alignment with ARMmbed/mbed-os-example-crash-reporting#65.

Fixes #14535

Author: LDong-Arm

tools/test/examples/examples.json

@@ -364,7 +364,7 @@
         "compile" : true,
         "export": true,
         "test" : true,
-        "baud_rate": 9600,
+        "baud_rate": 115200,
         "compare_log": ["mbed-os-example-crash-reporting/tests/crash-reporting.log"],
         "auto-update" : true
     },

tools/test/examples/examples_cmake.json

@@ -213,7 +213,7 @@
           "compile" : true,
           "export": true,
           "test" : true,
-          "baud_rate": 9600,
+          "baud_rate": 115200,
           "compare_log": ["mbed-os-example-crash-reporting/tests/crash-reporting.log"],
           "auto-update" : true
       },