docs: fix warnings for documentation build
docs: fix warnings for documentation build

"txt" is not a valid language to pass to "code-block" directives.
Passing "none" instead of "txt" would work; but there is no need to mark
the snippet as a "code-block" if no syntax highlighting is required,
simply using a literal block is enough.

Signed-off-by: Quentin Monnet <d6b8e48afb2534b213e391cab43016505747a234@isovalent.com>

tklauser/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium