Add known case with monorepos

content/code-security/dependabot/ecosystems-supported-by-dependabot/supported-ecosystems-and-repositories.md

@@ -44,3 +44,24 @@ You can configure updates for repositories that contain a dependency manifest or
 If your repository already uses an integration for dependency management, you will need to disable this before enabling {% data variables.product.prodname_dependabot %}. {% ifversion fpt or ghec %}For more information, see [AUTOTITLE](/get-started/exploring-integrations/about-integrations).{% endif %}
 
 {% data reusables.dependabot.supported-package-managers %}
+
+### Known issue: Tag format for GitHub Actions in monorepos
+
+If your repository contains multiple GitHub Actions (for example, in a monorepo), the tag format you use affects how {% data variables.product.prodname_dependabot %} detects and updates action versions.
+
+- **Dash (-) separator (e.g., `@my-action-v0.1.0`):**
+  - {% data variables.product.prodname_dependabot %} may group multiple actions under a single dependency entry or fail to detect new versions correctly. This occurs because {% data variables.product.prodname_dependabot %} relies on slash-based tag parsing to distinguish between actions.
+- **Slash (`/`) separator (e.g., `@my-action/v0.1.0`):**
+  - {% data variables.product.prodname_dependabot %} correctly detects and updates each action independently, as the slash creates a hierarchical tag structure that aligns with {% data variables.product.prodname_dependabot %}'s parsing logic.
+
+**Example**:
+```yaml
+# Recommended: namespaced with slash
+uses: my-org/monorepo/my-action@my-action/v0.1.0
+
+# Not recommended: dash
+uses: my-org/[email protected]
+```
+
+**Recommendation:**  
+For monorepos with multiple actions, use the `name/version` (slash) format for action tags. This ensures {% data variables.product.prodname_dependabot %} can parse the tag hierarchy correctly and update actions independently.