Test documentation typo fixes using codespell tool

Changes:
      - Fix typo in code documentation and test name

Tested: - Using codespell tool.

Change-Id: Ia1b65bddc01a4b1c103af9f2094d87da11c88953
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/lib/gen_robot_valid.py b/lib/gen_robot_valid.py
index d1e8d23..c25d9ab 100755
--- a/lib/gen_robot_valid.py
+++ b/lib/gen_robot_valid.py
@@ -73,7 +73,7 @@
         BuiltIn().fail(error_message)
 
 
-# The docstring header will be pre-pended to each validation function's existing docstring.
+# The docstring header will be prepended to each validation function's existing docstring.
 docstring_header = r"""
     Fail if the variable named by var_name is invalid.
     """