Update mantid dependency to latest Mantid stable 6.11

[jmborr]

Upgraded Mantid in conda.recipe meta.yaml from 6.8.0 to 6.11 and MantidWorkbench in environment.yml from 6.9.1 to 6.11. This ensures compatibility with the latest features and fixes provided in version 6.11.

Description of the changes

Check all that apply:

• added release notes (if not, provide an explanation in the work description)
• updated documentation
• Source added/refactored
• Added unit tests
• Added integration tests
• Verified that tests requiring the /SNS and /HFIR filesystems pass without fail

References:

• Links to IBM EWM items: 7905 (parent 7904)

Manual test for the reviewer

Check list for the reviewer

• release notes updated, or an explanation is provided as to why release notes are unnecessary
• best software practices
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date
• code comments added when explaining intent

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.87%. Comparing base (41009bb) to head (f67b2e0).
Report is 1 commits behind head on next.

Additional details and impacted files

@@           Coverage Diff           @@
##             next      #15   +/-   ##
=======================================
  Coverage   58.87%   58.87%           
=======================================
  Files           5        5           
  Lines         800      800           
=======================================
  Hits          471      471           
  Misses        329      329           

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