Rename glyph on hover is not legible

[binderjoe]

Testing #258212

When renaming a PR, the on-hover treatment for the edit button is low contrast and seems to have a single white pixel :(.

CC @jo-oikawa

[aiday-mar]

Hi may I ask what theme you are using here for the verification?

[sandy081]

I could verify that contrast is good on hover in various themes. But only thing which striked out to me was this small grey line in the pencil icon. Not sure if it is OK to to be fixed. Hence marking verified.

cc @alexr00