[updatecli] Bump Golang version to 1.21.8 (#133)

### What
Bump go release version with the latest release.

### Further details
See
[changelog](https://github.com/golang/go/issues?q=milestone%3AGo1.21.8+label%3ACherryPickApproved)
for 1.21.8
Generated automatically with
https://github.com/elastic/elastic-agent-system-metrics/actions/runs/8216878950


---



<Actions>
<action
id="901223529a6beca5c9cb3180f1dae9731c8da4e9c40169d7042cc0163a6d7e24">
        <h3>Bump golang-version to latest version</h3>
<details
id="1c5f933144e2a3bfbf48011624489c4d9255a0bd4a33c7fd95834f7ffbdbf77a">
            <summary>Update .go-version</summary>
<p>1 file(s) updated with &#34;1.21.8&#34;:&#xA;&#x9;*
.go-version&#xA;</p>
            <details>
                <summary>1.21.8</summary>
<pre>no GitHub Release found for go1.21.8 on
&#34;https://github.com/golang/go&#34;</pre>
            </details>
        </details>
<details
id="3b1d55e344f3f4bab100a1c68665344a238a102d31e80a9cc817751b6a853545">
            <summary>Update .golangci.yml</summary>
<p>1 file(s) updated with &#34;1.21.8&#34;:&#xA;&#x9;*
.golangci.yml&#xA;</p>
            <details>
                <summary>1.21.8</summary>
<pre>no GitHub Release found for go1.21.8 on
&#34;https://github.com/golang/go&#34;</pre>
            </details>
        </details>
    </action>
</Actions>

---

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      <p>
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href="https://www.updatecli.io/">Updatecli</a>
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---------

Co-authored-by: apmmachine <[email protected]>

.go-version

@@ -1 +1 @@
-1.21.7
+1.21.8

.golangci.yml

@@ -93,7 +93,7 @@ linters-settings:
 
   gosimple:
     # Select the Go version to target. The default is '1.13'.
-    go: "1.21.7"
+    go: "1.21.8"
 
   nakedret:
     # make an issue if func has more lines of code than this setting and it has naked returns; default is 30
@@ -113,17 +113,17 @@ linters-settings:
 
   staticcheck:
     # Select the Go version to target. The default is '1.13'.
-    go: "1.21.7"
+    go: "1.21.8"
     checks: ["all"]
 
   stylecheck:
     # Select the Go version to target. The default is '1.13'.
-    go: "1.21.7"
+    go: "1.21.8"
     checks: ["all"]
 
   unused:
     # Select the Go version to target. The default is '1.13'.
-    go: "1.21.7"
+    go: "1.21.8"
 
   gosec:
     excludes: