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/pldm/test_pldm_bios.robot b/pldm/test_pldm_bios.robot
index d62ea73..f2f0ca8 100755
--- a/pldm/test_pldm_bios.robot
+++ b/pldm/test_pldm_bios.robot
@@ -158,4 +158,4 @@
     ${date}=  Convert Date  ${date}  date_format=%b %d %H:%M:%S %Y
     ...  result_format=%Y-%m-%d %H:%M:%S  exclude_millis=True
 
-    [Return]   ${date}
+    RETURN   ${date}