Fix for Invalid Stripping for Email Message ID Parsing

[phutelmyer]

Describe the change
This change modifies the ScanEmail class in the strelka scanner module. The update involves a minor alteration where the message_id field is extracted from the email header without the surrounding angle brackets (<>) by using .strip rather than simply the removal of the first and last character.

The message_id to be parsed out is:
<DS7PR03MB5640AD212589DFB7CE58D90CFBEB9@DS7PR03MB5640.namprd03.prod.outlook.com>

Prior to fix, the message_id looked like this:
"message_id": "S7PR03MB5640AD212589DFB7CE58D90CFBEB9@DS7PR03MB5640.namprd03.prod.outlook.co"

After the fix, the message_id looks like this:
"message_id": "DS7PR03MB5640AD212589DFB7CE58D90CFBEB9@DS7PR03MB5640.namprd03.prod.outlook.com"

I did a bad job originally parsing it.

Describe testing procedures
scan_test_email.py was modified to pass based on the change

Sample output
N/A

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of and tested my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings