deps: update squidfunk/mkdocs-material docker tag to v9.5.8 (#3001)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

docs/Makefile

@@ -1,7 +1,7 @@
 ROOT_DIR := $(dir $(realpath $(lastword $(MAKEFILE_LIST))))
 
 # renovate: datasource=docker depName=squidfunk/mkdocs-material
-MKDOCS_DOCKER_IMAGE_VERSION=9.5.7
+MKDOCS_DOCKER_IMAGE_VERSION=9.5.8
 MKDOCS_DOCKER_IMAGE=squidfunk/mkdocs-material
 
 INTERACTIVE:=$(shell [ -t 0 ] && echo 1)