fix: deprecation warning for division in scss

Deprecation Warning: Using / for division outside of calc() is
deprecated and will be removed in Dart Sass 2.0.0.

Recommendation: math.div($header-height, 1.5) or calc($header-height / 1.5)

More info and automated migrator: https://sass-lang.com/d/slash-div

_sass/misc/article-menu.scss

@@ -16,7 +16,7 @@
   .post-menu-content {
     ul {
       border-left: 1px solid #e9ecef;
-      $indent: #{$base-font-size / 4};
+      $indent: calc($base-font-size / 4);
       $active-bgcolor: #ecebec;
 
       @for $i from 2 to 7 {

_sass/yat/_base.scss

@@ -42,7 +42,7 @@ h1, h2, h3, h4, h5, h6,
 p, blockquote, pre,
 ul, ol, dl, figure,
 %vertical-rhythm {
-  margin-bottom: #{$spacing-unit / 2};
+  margin-bottom: calc($spacing-unit / 2);
 }
 
 
@@ -128,7 +128,7 @@ a {
 blockquote {
   color: $grey-color;
   border-left: 4px solid $grey-color-light;
-  padding-left: #{$spacing-unit / 2};
+  padding-left: calc($spacing-unit / 2);
   @include relative-font-size(1.125);
   letter-spacing: -1px;
   font-style: italic;
@@ -222,7 +222,7 @@ table {
   }
 
   th, td {
-    padding: #{$spacing-unit / 3} #{$spacing-unit / 2};
+    padding: calc($spacing-unit / 3) calc($spacing-unit / 2);
   }
 
   th {

_sass/yat/_layout.scss

@@ -107,7 +107,7 @@ html {
 
     .site-favicon {
       display: inline-block;
-      height: #{$header-height / 1.5};
+      height: calc($header-height / 1.5);
       margin-right: 5px;
     }
   }
@@ -695,7 +695,7 @@ html {
   }
 
   @include media-query($on-palm) {
-    height: #{$banner-height / 1.5};
+    height: calc($banner-height / 1.5);
   }
 }