remove space before fenced codeblock info string.

[kivikakk]

Fixes #685. There's no reason for us to do this; we had copied the reference implementation, but I think it's nicer not to include the space.

[github-actions]

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
./bench.sh ./comrak-16213df	103.3 ± 0.9	101.6	105.7	1.77 ± 0.05
./bench.sh ./comrak-main	103.2 ± 0.9	101.4	105.0	1.77 ± 0.05
./bench.sh ./pulldown-cmark	58.2 ± 1.4	57.1	66.0	1.00
./bench.sh ./cmark-gfm	90.3 ± 8.1	81.2	104.7	1.55 ± 0.14
./bench.sh ./markdown-it	255.0 ± 3.9	245.5	262.9	4.38 ± 0.12

Run on Mon Nov 10 05:51:59 UTC 2025