fix(postgrest): ensure Sendable conformance for execute method

[grdsdev]

Summary

This PR addresses a compilation issue that occurs when using within a MainActor-isolated context. The method in has been updated to ensure conformance, allowing it to be safely used in concurrent environments.

Changes

• Modified to add conformance to the generic type in the method.
• Added to the file.

Testing

1. Compile the project with the updated code.
2. Verify that the compilation error related to conformance is resolved.

Fixes #739

[coveralls]

Pull Request Test Coverage Report for Build 16020601850

Details

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 75.68%

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Totals
Change from base Build 15556137759:	0.01%
Covered Lines:	5231
Relevant Lines:	6912

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💛 - Coveralls