[pre-commit.ci] pre-commit autoupdate (#5136)

* [pre-commit.ci] pre-commit autoupdate

updates:
- [github.com/asottile/blacken-docs: v1.12.1 → 1.13.0](adamchainz/blacken-docs@v1.12.1...1.13.0)

* Remove explicit black version dependency from blacken-docs.

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Martin Yeo <martin.yeo@metoffice.gov.uk>

.pre-commit-config.yaml

@@ -50,11 +50,10 @@ repos:
         args: [--filter-files]
 
 -   repo: https://github.com/asottile/blacken-docs
-    rev: v1.12.1
+    rev: 1.13.0
     hooks:
     -   id: blacken-docs
         types: [file, rst]
-        additional_dependencies: [black==21.6b0]
 
 -   repo: https://github.com/aio-libs/sort-all
     rev: v1.2.0