message: make shield on verification request scale correctly
  by not overriding `mask-size` using `mask` for `mask-image`
diff: @@ -25,7 +25,7 @@ limitations under the License.
  width: 12px;
  height: 16px;
  content: "";
  - mask: url("$(res)/img/e2e/normal.svg");
  + mask-image: url("$(res)/img/e2e/normal.svg");
  mask-repeat: no-repeat;
  mask-size: 100%;
  margin-top: 4px;
  @@ -33,7 +33,7 @@ limitations under the License.
  }
  &.mx_KeyVerification_icon_verified::after {
  - mask: url("$(res)/img/e2e/verified.svg");
  + mask-image: url("$(res)/img/e2e/verified.svg");
  background-color: $accent-color;
  }
  