Fix special tag formatting using "starts with"

The special formatting for the "spoiler" tag was being applied to a post
with the tag "spoiler attack", due to the way the CSS rules were
written. This still isn't a great solution overall, but should fix those
cases at least.

tildes/scss/modules/_label.scss

@@ -18,7 +18,9 @@
   max-width: 100%;
 }
 
-.label-topic-tag[class*='label-topic-tag-nsfw'],
-.label-topic-tag[class*='label-topic-tag-spoiler'] {
+.label-topic-tag-spoiler,
+.label-topic-tag-nsfw,
+.label-topic-tag[class*='label-topic-tag-nsfw-'],
+.label-topic-tag[class*='label-topic-tag-spoiler-'] {
   font-weight: bold;
 }

tildes/scss/themes/_theme_base.scss

@@ -312,11 +312,13 @@
     }
   }
 
-  .label-topic-tag[class*='label-topic-tag-nsfw'] {
+  .label-topic-tag-nsfw,
+  .label-topic-tag[class*='label-topic-tag-nsfw-'] {
     @include theme-special-label(map-get($theme, "topic-tag-nsfw"), $is-light);
   }
 
-  .label-topic-tag[class*='label-topic-tag-spoiler'] {
+  .label-topic-tag-spoiler,
+  .label-topic-tag[class*='label-topic-tag-spoiler-'] {
     @include theme-special-label(map-get($theme, "topic-tag-spoiler"), $is-light);
   }