fix (dashboard): Add content-type header (#3385)

### **PR Type**
Bug fix


___

### **Description**
- Add `Content-Type: application/json` header to GitHub app installation
request

- Ensure correct content type for POST request in dashboard

- Add changeset entry documenting the bug fix

- Improve API compatibility for GitHub app installation endpoint


___

### **Changes diagram**

```mermaid
flowchart LR
  A["GitHub App Installation Request"] -- "Add Content-Type header" --> B["API Endpoint"]
  B -- "Processes JSON body correctly" --> C["Improved Compatibility"]
```


___



### **Changes walkthrough** 📝
<table><thead><tr><th></th><th align="left">Relevant
files</th></tr></thead><tbody><tr><td><strong>Bug
fix</strong></td><td><table>
<tr>
  <td>
    <details>
<summary><strong>index.tsx</strong><dd><code>Add Content-Type header to
GitHub app installation POST request</code></dd></summary>
<hr>

dashboard/src/pages/github-app-installation/index.tsx

<li>Add <code>Content-Type: application/json</code> header to POST
request<br> <li> Ensure API receives correct content type for JSON body


</details>


  </td>
<td><a
href="https://github.com/nhost/nhost/pull/3385/files#diff-617a35daae6c458b9fe6374fe3d72a1f0c17f1975d2180ebed76d6945f8ced3c">+3/-0</a>&nbsp;
&nbsp; &nbsp; </td>

</tr>
</table></td></tr><tr><td><strong>Documentation</strong></td><td><table>
<tr>
  <td>
    <details>
<summary><strong>spicy-camels-work.md</strong><dd><code>Add changeset
entry for Content-Type header fix</code>&nbsp; &nbsp; &nbsp; &nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </dd></summary>
<hr>

.changeset/spicy-camels-work.md

- Add changeset entry describing the bug fix for dashboard


</details>


  </td>
<td><a
href="https://github.com/nhost/nhost/pull/3385/files#diff-ed215958071054c894c74606f2d96e18e5cc478183f88bebee13bce9e186e975">+5/-0</a>&nbsp;
&nbsp; &nbsp; </td>

</tr>
</table></td></tr></tr></tbody></table>

___

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.changeset/spicy-camels-work.md

@@ -0,0 +1,5 @@
+---
+'@nhost/dashboard': patch
+---
+
+fix (dashboard): Add content-type header

dashboard/src/pages/github-app-installation/index.tsx

@@ -45,6 +45,9 @@ function Page() {
           body: JSON.stringify({
             installationId,
           }),
+          headers: {
+            'Content-Type': 'application/json',
+          },
         });
       } catch (error) {
         setState({