Nested Vertical slides work, but slides are also shown in Horizontal Parent

[dpsifr]

Check that this is really a bug

• I confirm

Reproduction link

https://codesandbox.io/s/qw04s?file=/src/main.ts

Bug description

When I have nested vertical slides, everything works OK, but the nested slides also show up (double) in the parent slides.

`<swiper #outerSwiper direction="horizontal">
  <ng-template swiperSlide>
    <mat-card>
      <!-- additional content -->
    </mat-card>
  </ng-template>

  <ng-template swiperSlide>
    <mat-card>
      <!-- additional content -->
    </mat-card>
  </ng-template>

  <ng-template swiperSlide *ngFor="let slide of slides$ | async">
    <swiper #innerSwiper direction="vertical">
      <ng-container *ngFor="let innerSlide of slide.innerSlides>
        <ng-template swiperSlide>
          <mat-card class="papers stacks">
            <!-- additional content -->
          </mat-card>
        </ng-template>
      </ng-container>
    </swiper>
  </ng-template>
</swiper>`

When I get rid of all ng logic, I have the same problem which is why I was considering this a bug in Swiper.

<swiper direction="horizontal">
      <ng-template swiperSlide> test 1 </ng-template>
      <ng-template swiperSlide> test 2 </ng-template>
      <ng-template swiperSlide>
            <swiper direction="vertical">
                  <ng-template swiperSlide> test vertical 1 </ng-template>
                  <ng-template swiperSlide> test vertical 2 </ng-template>
           </swiper>
      </ng-template>
</swiper>

Expected Behavior

Nested vertical slides should not also appear in the parent horizontal slides.

Actual Behavior

Nested vertical slides are showing up both in the nested Swiper and the parent Swiper.

Swiper version

6.7.1

Platform/Target and Browser Versions

Chrome

Validations

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.
• Make sure this is a Swiper issue and not a framework-specific issue

Would you like to open a PR for this bug?

• I'm willing to open a PR