Use a string for the opengraph image and hopefully go to bed after that

Signed-off-by: Thib <thib@ergaster.org>

Author: thibaultamartin

content/blog/2026/05/2026-05-29-twim.md

@@ -8,7 +8,7 @@ author = ["Thib"]
 category = ["This Week in Matrix"]
 
 [extra]
-image = https://matrix.org/blog/img/2026-05-29-og.png
+image = "https://matrix.org/blog/img/2026-05-29-og.png"
 +++
 
 ## Matrix Live S12E09 – Element Demos