Bump minimum version to go 1.21.0 (#32451)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->

We currently use `go 1.21` in all go.mod files, this PR changes all
go.mod files to include the minor version by using `go 1.21.0`. It seems
that using the minor version is recommended by the Go project:
golang/go#62278. One of the dependencies in
collector-contrib also uses `go 1.21.0`, so this will need to be updated
eventually anyways: https://github.com/cilium/ebpf/blob/main/go.mod#L3.

**Link to tracking Issue:** <Issue number if applicable>

**Testing:** <Describe what testing was performed and which tests were
added.>

**Documentation:** <Describe the documentation added.>

---------

Co-authored-by: Antoine Toulme <[email protected]>

Author: liustanley

go.mod

@@ -1,6 +1,6 @@
 module github.com/open-telemetry/opentelemetry-collector-contrib/receiver/k8sobjectsreceiver
 
-go 1.21
+go 1.21.0
 
 require (
 	github.com/google/uuid v1.6.0