fix: bump aws-sdk-go-v2 SDKs for AWS European Sovereign Cloud (EUSC) support

[nlang]

Summary

• Bump service/sso v1.22.1 → v1.30.16 and service/ssooidc v1.26.2 → v1.35.20 (plus required transitive aws-sdk-go-v2 core / smithy-go / internal/configsources / internal/endpoints/v2 bumps).
• These SDK versions add the aws-eusc partition with the correct DNS suffix amazonaws.eu and the regex ^eusc-(de)-\w+-\d+$. Without it, the SDK falls back to amazonaws.com and DNS resolution for EUSC endpoints (e.g. oidc.eusc-de-east-1.amazonaws.com) fails.
• The new SDK modules require Go 1.24, so the go directive in go.mod is raised from 1.23 to 1.24.
• No code changes — ssooidc.New(...) / sso.New(...) already let the SDK resolve the partition from the region.

Motivation

End users in the EU Sovereign Cloud (region eusc-de-east-1) currently hit:

dial tcp: lookup oidc.eusc-de-east-1.amazonaws.com: no such host
dial tcp: lookup portal.sso.eusc-de-east-1.amazonaws.com: no such host

because the vendored SDKs predate the aws-eusc partition.

Test plan

• go build ./... clean
• go test ./... all packages pass
• go vet ./... clean
• End-to-end verified by the reporter: RegisterClient and StartDeviceAuthorization against eusc-de-east-1 now resolve to *.amazonaws.eu and the device authorization flow completes.

Note on Go version

go.mod is bumped to go 1.24 because the upgraded SDK modules declare it as their minimum. If vars.GO_VERSION in CI is still below 1.24, it will need to be raised together with this change.

[synfinatic]

@nlang gonna need you to rebase as we're now on GO 1.26.3. github worker issue :(. seems GH stability is biting us here... give it some time and will try again for this and your other PR.

[synfinatic]

@nlang can you rebase?

[nlang]

done :)

[synfinatic]

@nlang sorry, one more time (this and your other PR). removed all the github vars from the workflows which were breaking the build since github won't pass them into PR's from a fork.

[nlang]

sure, here you go ;)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.85%. Comparing base (da16a7f) to head (f627eb7).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1309   +/-   ##
=======================================
  Coverage   84.85%   84.85%           
=======================================
  Files          44       44           
  Lines        3465     3465           
=======================================
  Hits         2940     2940           
  Misses        422      422           
  Partials      103      103           

Flag	Coverage Δ
unittests	84.85% <ø> (ø)

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