treewide: Fix all Nix ASTs in all markdown files

This allows for correct highlighting and maybe future automatic
formatting. The AST was verified to work with nixfmt only.

doc/languages-frameworks/php.section.md

@@ -97,7 +97,7 @@ let
   myPhp = php.withExtensions ({ all, ... }: with all; [ imagick opcache ]);
 in {
   services.phpfpm.pools."foo".phpPackage = myPhp;
-};
+}
 ```
 
 ```nix
@@ -108,7 +108,7 @@ let
   };
 in {
   services.phpfpm.pools."foo".phpPackage = myPhp;
-};
+}
 ```
 
 #### Example usage with `nix-shell` {#ssec-php-user-guide-installing-with-extensions-nix-shell}
@@ -149,7 +149,7 @@ php.override {
     extensions = prev.extensions // {
       mysqlnd = prev.extensions.mysqlnd.overrideAttrs (attrs: {
         patches = attrs.patches or [] ++ [
-          …
+          # ...
         ];
       });
     };