Fix purple color in suggested label colors (go-gitea#18241)

This looks like a typo that was introduced when these colors were added,
causing what is supposed to be purple show up as green.

Author: silverwind

templates/repo/issue/label_precolors.tmpl

@@ -5,7 +5,7 @@
 <a class="color" style="background-color:#006b75" data-color-hex="#006b75"></a>
 <a class="color" style="background-color:#207de5" data-color-hex="#207de5"></a>
 <a class="color" style="background-color:#0052cc" data-color-hex="#0052cc"></a>
-<a class="color" style="background-color:#53e917" data-color-hex="#53e917"></a>
+<a class="color" style="background-color:#5319e7" data-color-hex="#5319e7"></a>
 <a class="color" style="background-color:#f6c6c7" data-color-hex="#f6c6c7"></a>
 <a class="color" style="background-color:#fad8c7" data-color-hex="#fad8c7"></a>
 <a class="color" style="background-color:#fef2c0" data-color-hex="#fef2c0"></a>