fix(fmt/markdown): metadata header sometimes missing trailing blank line (#25141)

* dprint/dprint-plugin-markdown#119

Author: dsherret

.dprint.json

@@ -67,7 +67,7 @@
   "plugins": [
     "https://plugins.dprint.dev/typescript-0.91.6.wasm",
     "https://plugins.dprint.dev/json-0.19.3.wasm",
-    "https://plugins.dprint.dev/markdown-0.17.5.wasm",
+    "https://plugins.dprint.dev/markdown-0.17.6.wasm",
     "https://plugins.dprint.dev/toml-0.6.2.wasm",
     "https://plugins.dprint.dev/exec-0.5.0.json@8d9972eee71fa1590e04873540421f3eda7674d0f1aae3d7c788615e7b7413d0",
     "https://plugins.dprint.dev/g-plane/pretty_yaml-v0.4.0.wasm"

Cargo.lock

@@ -102,7 +102,7 @@ dissimilar = "=1.0.4"
 dotenvy = "0.15.7"
 dprint-plugin-json = "=0.19.3"
 dprint-plugin-jupyter = "=0.1.3"
-dprint-plugin-markdown = "=0.17.5"
+dprint-plugin-markdown = "=0.17.6"
 dprint-plugin-typescript = "=0.91.6"
 env_logger = "=0.10.0"
 fancy-regex = "=0.10.0"