[Form] Fixed: "required" attribute is not added to <select> tag if no empty value
merged branch bschussek/issue8942 (PR #9030)

This PR was merged into the 2.3 branch.

Discussion
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[Form] Fixed: "required" attribute is not added to <select> tag if no empty value

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8942
| License       | MIT
| Doc PR        | -

Commits
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a273e79 [Form] Fixed: "required" attribute is not added to <select> tag if no empty value