all: Upgrade go.opentelemetry.io/otel/sdk to v1.40.0

[cezarmathe]

This PR upgrades go.opentelemetry.io/otel/sdk to v1.40.0 to mitigate GO-2026-4394.

[vangent]

Sorry, can you merge and run "go mod tidy"?

[vangent]

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• Running Go tests for module: secrets/hashivault

---

go: updates to go.mod needed; to update it:
go mod tidy
ran 0; passed 0; failed 0; skipped 0 (in 0.0 sec)

FAILED; see above for more info.
Error: Process completed with exit code 1.

[cezarmathe]

My bad! I've just realized that go-cloud uses multiple submodules. I've upgraded all of them.

I've also added a handy script to upgrade a dependency in all dependent submodules, do you mind? Here's a usage example:

$ ./contrib/upgrade-dependency.sh go.opentelemetry.io/otel

Upgrading "go.opentelemetry.io/otel".
Module files to adjust: runtimevar/hashivault/go.mod, runtimevar/etcdvar/go.mod, secrets/hashivault/go.mod, pubsub/kafkapubsub/go.mod, go.mod, docstore/mongodocstore/go.mod, samples/go.mod, pubsub/rabbitpubsub/go.mod, pubsub/natspubsub/go.mod.
Upgrading "go.opentelemetry.io/otel" in "runtimevar/hashivault".
+ cd runtimevar/hashivault
+ go get -u go.opentelemetry.io/otel
+ go mod tidy
+ cd redacted
+ set +x
Upgrading "go.opentelemetry.io/otel" in "runtimevar/etcdvar".
+ cd runtimevar/etcdvar
+ go get -u go.opentelemetry.io/otel
+ go mod tidy
+ cd redacted
+ set +x
Upgrading "go.opentelemetry.io/otel" in "secrets/hashivault".
+ cd secrets/hashivault
+ go get -u go.opentelemetry.io/otel
+ go mod tidy
+ cd redacted
+ set +x
Upgrading "go.opentelemetry.io/otel" in "pubsub/kafkapubsub".
+ cd pubsub/kafkapubsub
+ go get -u go.opentelemetry.io/otel
+ go mod tidy
+ cd /Users/cezar-fm/code/go-cloud
+ set +x
Upgrading "go.opentelemetry.io/otel" in ".".
+ cd .
+ go get -u go.opentelemetry.io/otel
+ go mod tidy
+ cd redacted
+ set +x
Upgrading "go.opentelemetry.io/otel" in "docstore/mongodocstore".
+ cd docstore/mongodocstore
+ go get -u go.opentelemetry.io/otel
+ go mod tidy
+ cd redacted
+ set +x
Upgrading "go.opentelemetry.io/otel" in "samples".
+ cd samples
+ go get -u go.opentelemetry.io/otel
+ go mod tidy
+ cd redacted
+ set +x
Upgrading "go.opentelemetry.io/otel" in "pubsub/rabbitpubsub".
+ cd pubsub/rabbitpubsub
+ go get -u go.opentelemetry.io/otel
+ go mod tidy
+ cd redacted
+ set +x
Upgrading "go.opentelemetry.io/otel" in "pubsub/natspubsub".
+ cd pubsub/natspubsub
+ go get -u go.opentelemetry.io/otel
+ go mod tidy
+ cd redacted
+ set +x