[Form] Fix of "PATCH'ed forms are never valid"

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8111
| License       | MIT
merged branch biozshock/patch-form-fix (PR #8362)

This PR was merged into the 2.3 branch.

Discussion
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[Form] Fix of "PATCH'ed forms are never valid". Fixes #8111

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8111
| License       | MIT

Commits
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a2b1535 [Form] Fix of "PATCH'ed forms are never valid"