[pre-commit.ci] auto fixes from pre-commit.com hooks

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Author: pre-commit-ci[bot]

docs/maintainer/pinning_deps.md

@@ -54,6 +54,7 @@ requirements:
 The run-export mechanism (see below) additionally ensures the correct version constraints
 (corresponding to the expected API/ABI stability of `gmp`) are added, so a recipe with an
 unpinned `gmp` dependency in the host environment will, in the end, work as follows:
+
 ```yaml
 requirements:
   host: