I am afraid I cannot replicate in a fresh environment:
$ go clean -modcache
$ go mod init github.com/temporalio/temp
go: creating new go.mod: module github.com/temporalio/temp
$ go get go.temporal.io/sdk@v1.10.0
go: downloading go.temporal.io/sdk v1.10.0
go get: added go.temporal.io/sdk v1.10.0
$ grep temporal go.sum
go.temporal.io/api v1.5.0/go.mod h1:BqKxEJJYdxb5dqf0ODfzfMxh8UEQ5L3zKS51FiIYYkA=
go.temporal.io/sdk v1.10.0 h1:JfzXWB+/EcDcC6poz6/k0dc57qas+Es1LMcIXEvP8IA=
go.temporal.io/sdk v1.10.0/go.mod h1:J3kkGHdnPCyPhGO3dsijYNTUE7JgX51vJmjKJY4BF8c=
Do you happen to have any other environments you can test on? Might there be some proxy set (either in the OS or via the GOPROXY env var) or something else intercepting traffic?