all: Regenerate expired interop test TLS certificates

[nicholaspcr]

Summary

The TLS test certificates in pkg/interop/testdata/ expired on 2026-04-08, causing TestGetAppSKey/Backend_Interfaces_1.0/UnknownDevEUI to fail with x509: certificate has expired or is not yet valid.

Changes

• Regenerated server and client TLS certificates and keys using CAROOT=. go generate . in pkg/interop/testdata/.
• New certificates are valid until 2028-07-14.

Testing

Steps

Run the previously failing test:

go test ./pkg/interop/... -run "TestGetAppSKey/Backend_Interfaces_1.0/UnknownDevEUI" -count=1

Results

Test passes after certificate regeneration:

ok  	go.thethings.network/lorawan-stack/v3/pkg/interop	0.834s

Regressions

No regressions expected. Only test certificate files were changed; no production code was modified.

Notes for Reviewers

Certificates were regenerated using the existing go generate directives in pkg/interop/testdata/testdata.go with CAROOT=. to use the local root CA already in the testdata directory.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• Testing: The steps/process to test this feature are clearly explained including testing for regressions.
• Infrastructure: If infrastructural changes (e.g., new RPC, configuration) are needed, a separate issue is created in the infrastructural repositories.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.