Bump fsdocs-tool from 20.0.0-alpha-012 to 20.0.0-alpha-013

Bumps [fsdocs-tool](https://github.com/fsprojects/FSharp.Formatting) from 20.0.0-alpha-012 to 20.0.0-alpha-013.
- [Changelog](https://github.com/fsprojects/FSharp.Formatting/blob/main/RELEASE_NOTES.md)
- [Commits](https://github.com/fsprojects/FSharp.Formatting/commits)

---
updated-dependencies:
- dependency-name: fsdocs-tool
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.config/dotnet-tools.json

@@ -15,7 +15,7 @@
       ]
     },
     "fsdocs-tool": {
-      "version": "20.0.0-alpha-012",
+      "version": "20.0.0-alpha-013",
       "commands": [
         "fsdocs"
       ]