go.mod: change version from 1.23 to 1.23.0

1.23 is not a downloable release. Go mod should list the specific
toolchain that can be downloaded as mentioned here:
golang/go#62278 (comment)
Otherwise opening the project having a different version installed will
result in errors, e.g:

```
$ go version
go: downloading go1.23 (linux/amd64)
go: download go1.23 for linux/amd64: toolchain not available
```

Signed-off-by: Antonio Gutierrez <antonio.gutierrez1@ibm.com>

go.mod

@@ -1,6 +1,6 @@
 module github.com/instana/instana-agent-operator
 
-go 1.23
+go 1.23.0
 
 require (
 	github.com/Masterminds/goutils v1.1.1