[Form] Improved test coverage of UrlType
minor #10647 [Form] Improved test coverage of UrlType (webmozart)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #10647).

Discussion
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[Form] Improved test coverage of UrlType

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
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f3e172f [Form] Improved test coverage of UrlType