Robot Framework 7.0 changes

Update robot code syntax overall in the repo

Changes:
   - Update the requirement.txt package version for robot
   - The '[Return]' setting is deprecated.
      Use the 'RETURN' statement instead.
   - Singular section headers like '*** Test Case ***'
     are deprecated. Use plural format like
     '*** Test Cases ***' instead.
   - Singular section headers like '*** Variable ***'
     are deprecated

Tested:
   - Ran from sandbox with the version
     $ robot --version
     Robot Framework 7.0 (Python 3.10.12 on linux)

     and also tested on latest python version

     Robot Framework 7.0 (Python 3.11.9 on linux)

Change-Id: I54e85f9d799556c63b9a39f79483f83e9b980768
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/redfish/dmtf_tools/Redfish_Reference_Checker.robot b/redfish/dmtf_tools/Redfish_Reference_Checker.robot
index 1911171..92f2c3b 100644
--- a/redfish/dmtf_tools/Redfish_Reference_Checker.robot
+++ b/redfish/dmtf_tools/Redfish_Reference_Checker.robot
@@ -20,7 +20,7 @@
 
 ${branch_name}    main
 
-*** Test Case ***
+*** Test Cases ***
 
 Test BMC Redfish Reference
     [Documentation]  Checks for valid reference URLs in CSDL XML files.