chore(deps): update dependency go to v1.21.5 (#34)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [go](https://go.dev/) ([source](https://togithub.com/golang/go)) |
golang | patch | `1.21.4` -> `1.21.5` |

---

### Release Notes

<details>
<summary>golang/go (go)</summary>

###
[`v1.21.5`](https://togithub.com/golang/go/compare/go1.21.4...go1.21.5)

</details>

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exporter/discordexporter/go.mod

@@ -1,6 +1,6 @@
 module github.com/ymotongpoo/opentelemetry-collector-extra/exporter/discordexporter
 
-go 1.21.4
+go 1.21.5
 
 require (
 	github.com/bwmarrin/discordgo v0.27.1

receiver/discordreceiver/go.mod

@@ -1,6 +1,6 @@
 module github.com/ymotongpoo/opentelemetry-collector-extra/receiver/discordreceiver
 
-go 1.21.4
+go 1.21.5
 
 require (
 	github.com/bwmarrin/discordgo v0.27.1

receiver/slackreceiver/go.mod

@@ -1,6 +1,6 @@
 module github.com/ymotongpoo/opentelemetry-collector-extra/receiver/slackreceiver
 
-go 1.21.4
+go 1.21.5
 
 require (
 	github.com/google/go-cmp v0.6.0