fix DDOC_AUTO_{PSYMBOL,KEYWORD,PARAM}

Fixes issue 18709.

Author: aG0aep6G

changelog/2.079.0.dd

@@ -405,9 +405,9 @@ that they simply expand to the word itself without any highlighting:
 )
 
 ----
-DDOC_AUTO_PSYMBOL = $0
-DDOC_AUTO_KEYWORD = $0
-DDOC_AUTO_PARAM = $0
+DDOC_AUTO_PSYMBOL = $(DOLLAR)0
+DDOC_AUTO_KEYWORD = $(DOLLAR)0
+DDOC_AUTO_PARAM = $(DOLLAR)0
 ----
 
 $(P

dlang.org.ddoc

@@ -554,8 +554,8 @@ FA_ICON=<i class="fa fa-$1" aria-hidden="true"></i>
 _=
 
 _ = Opt-out of automatic keyword highlighting - see https://dlang.org/changelog/2.079.0.html#fix18361
-DDOC_AUTO_PSYMBOL =
-DDOC_AUTO_KEYWORD =
-DDOC_AUTO_PARAM =
+DDOC_AUTO_PSYMBOL = $0
+DDOC_AUTO_KEYWORD = $0
+DDOC_AUTO_PARAM = $0
 _ = DDOC_AUTO_PSYMBOL_SUPPRESS = FIXME_UNDERSCORE_PREFIX
 DDOC_AUTO_PSYMBOL_SUPPRESS = $1