utils/getdeveloperlib.py: fix retrieve typo

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

utils/getdeveloperlib.py

@@ -85,7 +85,7 @@ def get_all_test_cases(suite):
 
 
 def list_unittests():
-    """Use the unittest module to retreive all test cases from a given
+    """Use the unittest module to retrieve all test cases from a given
     directory"""
     loader = unittest.TestLoader()
     suite = loader.discover(os.path.join(brpath, "support", "testing"))