Certain characters are incorrectly escaped when rendering custom links

[jeremystretch]

NetBox version

v3.4.9

Python version

3.8

Steps to Reproduce

1. Create a custom link with the URL http://example.com/?foo=1&bar=2
2. View an object where the custom link appears and inspect its source

Expected Behavior

The unmodified URL should be present.

Observed Behavior

The link is incorrectly escaped to http://example.com/?foo%3D1&bar%3D2. This is a regression resulting from 89fa546.