Move build to Go 1.21

[yurishkuro]

Which problem is this PR solving?

• Move to next Go version per maintenance policy (see Implement N-1 support policy for Go versions #4653)

Description of the changes

Ran the script

$ ./scripts/check-go-version.sh -u
go.mod                                             Go version: 1.20
docker/Makefile                                    Go version: 1.20 *** => 1.21 ***
.github/workflows/fossa.yml                        Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-release.yml                   Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-unit-tests.yml                Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-docker-build.yml              Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-build-binaries.yml            Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-crossdock.yml                 Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-elasticsearch.yml             Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-grpc-badger.yml               Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-hotrod.yml                    Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-protogen-tests.yml            Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-all-in-one-build.yml          Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-cassandra.yml                 Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-opensearch.yml                Go version: 1.20 *** => 1.21 ***
.github/workflows/ci-kafka.yml                     Go version: 1.20 *** => 1.21 ***
.golangci.yml                                      Go version: 1.20
15 file(s) updated.

[codecov]

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