doc: format config values with backticks #26595

Job	Run time
config	9s
static-analysis	0s
sparse	0s
win+Meson build	0s
win build	0s
win+Meson test	0s
win test	0s
${{ matrix.vector.jobname }} (${{ matrix.vector.image }})	0s
win+VS build	0s
${{ matrix.vector.jobname }} (${{ matrix.vector.pool }})	0s
documentation	0s
fuzz smoke test	0s
rust-analysis	0s
win+VS test	0s
	9s

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