Noto Serif SC webfont misses glyphs for U+2018 and U+2019

Specify the font name in title with a short description of the bug.
~~Please report any issue related to Noto fonts [here](https://notofonts.github.io/reporter.html).~~
**This is *not* a Noto fonts issue, as the downloaded OTF file doesn't have this issue. Only the webfont has this issue.**
Report any issue with Google Icon/Symbols [here](https://github.com/google/material-design-icons)

**Describe the bug**
Noto Serif SC webfont misses glyphs for U+2018 (left single quotation mark) and U+2019 (right single quotation mark).

**To Reproduce**
Open [this](https://fonts.google.com/noto/specimen/Noto+Serif+SC?preview.text=%E2%80%98%E2%80%99&preview.text_type=custom) and see the preview under *Styles*.

**Expected behavior**
There should be no tofu, and all the quotation marks should be full-width.

**Screenshots**

**Additional context**
Strangely, only the regular variant appears as tofu at first. When you click on any other variant, they become tofu too. When included as webfonts in a webpage, none of the variants include the two code points.