Rename SASS tests to SCSS, since they're using SCSS syntax

tests/syntax-tests/source/SCSS/LICENSE.md

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+This file has been copied from https://sass-lang.com/documentation/syntax
+
+
+LICENSE:
+
+
+Copyright (c) 2006-2018 Hampton Catlin, Natalie Weizenbaum, Chris Eppstein, and
+Jina Anne
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

tests/syntax-tests/source/SCSS/example.scss

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+@mixin button-base() {
+  @include typography(button);
+  @include ripple-surface;
+  @include ripple-radius-bounded;
+
+  display: inline-flex;
+  position: relative;
+  height: $button-height;
+  border: none;
+  vertical-align: middle;
+
+  &:hover { cursor: pointer; }
+
+  &:disabled {
+    color: $mdc-button-disabled-ink-color;
+    cursor: default;
+    pointer-events: none;
+  }
+}