fix: updated mocha tests to display error messages

[btw17]

The basics

• I validated my changes

The details

Resolves

Fixes #7649

Proposed Changes

Instead of using getText(), which requires a visible element, I use getHTML() and strip out the p tag.
- See https://webdriver.io/docs/api/element/getText and note: only visible elements will return display.
- The root element with id failureCount has display: none, so the text content here never displays.

Previous output:

Loading URL: file:///usr/local/google/home/blaketw/git/blockly/blockly/tests/mocha/index.html
============Blockly Mocha Test Failures================

============Blockly Mocha Test Summary=================
1 tests failed
============Blockly Mocha Test Summary=================
Mocha tests failed

Updated output:

Loading URL: file:///usr/local/google/home/blaketw/git/blockly/blockly/tests/mocha/index.html
============Blockly Mocha Test Failures================
"Comments Set/Get Bubble Size Set Size While Invisible" failed: expected 100 to equal 101
============Blockly Mocha Test Summary=================
1 tests failed
============Blockly Mocha Test Summary=================
Mocha tests failed

Reason for Changes

To resolve #7649

Test Coverage

N/A

Documentation

N/A

Additional Information

• Not sure if #failureCount was previously visible, though another way to mitigate this would be to set it visible

[maribethb]

nit: could you replace the double quotes with single quotes? it appears we don't format this file but that would match the rest of the file. Thanks!

[btw17]

Done!