docs: Fix repository path for telling git it's safe
docs: Fix repository path for telling git it's safe

It seems that git does not expand paths when looking for safe
repositories in its config file. So the following does not work:

    git config --global --add safe.directory /src/Documentation/..

Instead we need the regular path:

    git config --global --add safe.directory /src

Take $(dirname Documentation) to mark the correct path.

Fixes: df17a7c969c6 ("docs: Mark Git repo as safe (if in container) before spell checks")
Signed-off-by: Quentin Monnet <d6b8e48afb2534b213e391cab43016505747a234@isovalent.com>

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