Upgrade the spin sdk for golang to 0.6.0

[qnm]

Using an up-to-date Go / Tinygo with make spin serve results in the error described in https://github.com/fermyon/spin/issues/624 as the kitchensink repo uses a particularly old version of the spin sdk.

This PR updates the go dependencies to the latest stable sdk version.

This should also fix https://github.com/fermyon/spin-kitchensink/issues/17

[itowlson]

@qnm Thanks for this! Before we merge, is there any particular reason for going to 0.4.0 rather than 0.6.0? There were some changes between the two I think.

[qnm]

@itowlson None - it was the closest to the original. Let me revise with 0.6.0 and verify.

[qnm]

@itowlson I've adjusted the SDK version to 0.6.0 as suggested.