PR: Improve appearance of breakpoint icon

[ccordoba12]

This is a little improvement after PR #5283.

The first breakpoint in the screenshots below is only shown when the mouse is on hover over the panel and the second one is a set breakpoint.

Before

After

[pep8speaks]

Hello @ccordoba12! Thanks for submitting the PR.

• In the file spyder/utils/icon_manager.py, following are the PEP8 issues :

Line 99:80: E501 line too long (108 > 79 characters)
Line 100:80: E501 line too long (92 > 79 characters)
Line 100:90: E202 whitespace before ']'
Line 101:80: E501 line too long (101 > 79 characters)
Line 101:99: E231 missing whitespace after ','