Fix typos related to MessageDialog API

[nvdaes]

• Fix typo in _modalDialogOpenCallback method
• Developer guide: fix capitalization for ReturnCode in confirm meth of MessageDialog documentation

Link to issue number:

None

Summary of the issue:

When a modal message dialog is open and we tried to use blocked actions like opening the NVDA's menu or the exit dialog, an error is raised

Description of user facing changes

Description of development approach

• Fixed tipo in _modalDialogOpenCallback method of source/gui/blockAction.py.
• Additionally, fixed capitalization of the confirm method in the developer guide.

Testing strategy:

Tested locally with clipContentsDesigner add-on, version 45.0.1 (dev channel), and opening message dialogs in the Python console, trying to activate the NVDA's menu or the exit dialog.

Known issues with pull request:

None

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.

@coderabbitai summary

[AppVeyorBot]

• PASS: Translation comments check.
• PASS: License check.
• PASS: Unit tests.
• PASS: Lint check.
• FAIL: System tests (tags: installer NVDA). See test results for more information.
• Build (for testing PR): https://ci.appveyor.com/api/buildjobs/mmvncsi7wt6yh663/artifacts/output/nvda_snapshot_pr17612-34996,dd286fcb.exe
• CI timing (mins):
  INIT 0.0,
  INSTALL_START 1.1,
  INSTALL_END 0.8,
  BUILD_START 0.0,
  BUILD_END 23.4,
  TESTSETUP_START 0.0,
  TESTSETUP_END 0.3,
  TEST_START 0.0,
  TEST_END 18.3,
  FINISH_END 0.2

See test results for failed build of commit dd286fcb47

[nvdaes]

@SaschaCowley , I think that failure in system tests is not related to this PR.

[SaschaCowley]

Thanks, @nvdaes