Download GitHub database: fix gh invocation

At least as of GitHub CLI v2.13.0, the leading slash in `gh api /repos/...` leads to a 404. In all GitHub CLI versions, the trailing slash of `gh api .../databases/` seems to not be acceptable, either.

Author: dscho

docs/codeql/reusables/download-github-database.rst

@@ -3,12 +3,12 @@ GitHub stores CodeQL databases for over 200,000 repos on GitHub.com, which you c
 You can check if a repository has any CodeQL databases available for download using the ``/repos/<owner>/<repo>/code-scanning/codeql/databases`` endpoint.
 For example, to check for CodeQL databases using the `GitHub CLI <https://cli.github.com/manual/gh_api>`__ you would run::
 
-   gh api /repos/<owner>/<repo>/code-scanning/codeql/databases/
+   gh api repos/<owner>/<repo>/code-scanning/codeql/databases
 
 This command returns information about any CodeQL databases that are available for a repository, including the language the database represents, and when the database was last updated. If no CodeQL databases are available, the response is empty.
 
 When you have confirmed that a CodeQL database exists for the language you are interested in, you can download it using the following command::
 
-   gh api /repos/<owner>/<repo>/code-scanning/codeql/databases/<language> -H 'Accept: application/zip' > path/to/local/database.zip
+   gh api repos/<owner>/<repo>/code-scanning/codeql/databases/<language> -H 'Accept: application/zip' > path/to/local/database.zip
 
 For more information, see the documentation for the `Get CodeQL database <https://docs.github.com/en/rest/code-scanning#get-a-codeql-database-for-a-repository>`__ endpoint in the GitHub REST API documentation.