Check default browser dialog has the invalid background style property

[luixxiul]

Test plan

#11044 (comment)

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Description

Check default browser dialog does not have the valid background style property.

Steps to Reproduce

1. Change the default browser from Brave
2. Open Brave
3. Open the devtool on the browser level

Actual result:

browser-laptop/app/renderer/components/main/checkDefaultBrowserDialog.js

Lines 121 to 122 in 795f36a

	section__braveIcon: {
	backgroundImage: `image-set(url(${braveAbout}) 2x)`,

Expected result:
backgroundImage: -webkit-image-set(url(${braveAbout}) 2x),

Reproduces how often: [What percentage of the time does it reproduce?]
Always

Brave Version

Brave: 0.19.7
rev: c8481a9
Muon: 4.4.16
libchromiumcontent: 61.0.3163.71
V8: 6.1.534.31
Node.js: 7.9.0
Update Channel: Beta
OS Platform: Linux
OS Release: 4.9.0-3-amd64
OS Architecture: x64

Additional Information

Introduced by me with #8443