support/testing: basetest.py: fix code style

Fix these warnings:

W291 trailing whitespace

Fixes:
 - https://gitlab.com/buildroot.org/buildroot/-/jobs/360824861

Signed-off-by: Pierre-Jean Texier <pjtexier@koncepto.io>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

support/testing/infra/basetest.py

@@ -85,7 +85,7 @@ class BRTest(BRConfigTest):
             self.emulator.stop()
         super(BRTest, self).tearDown()
 
-    # Run the given 'cmd' with a 'timeout' on the target and 
+    # Run the given 'cmd' with a 'timeout' on the target and
     # assert that the command succeeded
     def assertRunOk(self, cmd, timeout=-1):
         _, exit_code = self.emulator.run(cmd, timeout)