doc: fix yaml indentation typo that broke building the website

docs/yaml/functions/install_emptydir.yaml

@@ -19,9 +19,9 @@ kwargs:
       group/gid for the created directory.
 
       See the `install_mode` kwarg of [[install_data]] for more information.
-    install_tag:
-      type: str
-      description: |
-        A string used by the `meson install --tags` command to install only a
-        subset of the files. By default this directory has no install tag which
-        means it is not installed when the `--tags` argument is specified.
+  install_tag:
+    type: str
+    description: |
+      A string used by the `meson install --tags` command to install only a
+      subset of the files. By default this directory has no install tag which
+      means it is not installed when the `--tags` argument is specified.