Fix go.mod go version to 1.20

[gonzaloserrano]

What type of PR is this?

/kind bug

What this PR does / why we need it:

I tried running guest/ tests with go 1.20.x and got

internal/imports/mem.go:24:24: unsafe.StringData requires go1.20 or later (-lang was set to go1.19; check go.mod)

Then I downgraded to go 1.19 (via brew) and got:

# sigs.k8s.io/kube-scheduler-wasm-extension/guest/internal/imports
internal/imports/mem.go:24:31: undefined: unsafe.StringData

So since unsafe.StringData is from go 1.20 I guess the guest go.mod should specify go 1.20? Most of the repo versions, and kubernetes/kubernetes also, have go 1.20 in their go.mod.

Which issue(s) this PR fixes:

n/a

Special notes for your reviewer:

n/a

Does this PR introduce a user-facing change?

NONE

[k8s-ci-robot]

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[codefromthecrypt]

There are no tests in the guest module, so I think the impact of this is lower.

We are intentionally leaving the guest (tinygo) as 1.19 until TinyGo 0.28 which supports 1.20 is out (very soon). We should probably add a comment to the go.mod that this is for tinygo.

[kerthcet]

/hold
Feel free to close this or hold until tinygo releases v0.28.