Fixed bug that incorrectly causes the "required" attribute to be omitted from select even though it contains the "multiple" attribute
bug #10491 Fixed bug that incorrectly causes the "required" attribute to be omitted from select even though it contains the "multiple" attribute (fabpot)

This PR was submitted for the 2.4 branch but it was merged into the 2.3 branch instead (closes #10491).

Discussion
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Fixed bug that incorrectly causes the "required" attribute to be omitted from select even though it contains the "multiple" attribute

According to the HTML5 specification the required attribute should be allowed in this case: "A select element with a required attribute and **without** a multiple attribute, and whose size is “1”, must have a child option element."

Related PR: https://github.com/symfony/symfony/pull/9030

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

Commits
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f9aa676 Fixed bug that incorrectly causes the "required" attribute to be omitted from select even though it contains the "multiple" attribute