Fix @NotNull to apply to payload field, not payload type

[benjie]

Fixes #1595

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Latest commit: b7b6dd64fcc07f2ca15528fd39d61297d743dcc6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

| Name | Type | | ----------------- | ----- | | graphile-build-pg | Patch | | postgraphile | Patch | | graphile-utils | Patch | | pgl | Patch | | graphile | Patch |

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