Aşağıdaki gibi hallettim. "product-inner*-item" kısmına "gridsistemi" diye bir css koydum ve halloldu. Cevaplar için teşekkürler.

<div class="new-product-slider owl-carousel owl-nav-style">

    <?php
    $yenigelenurunekle_index_sorgusu = "SELECT * FROM yenigelenurunekle LIMIT 8";
    $yenigelenurunekle_index_sorgusu_query = mysqli_query($db, $yenigelenurunekle_index_sorgusu);
    ?>

    <div class="product-inner-item gridsistemi">
        <?php foreach($yenigelenurunekle_index_sorgusu_query as $yenigelenurunekle_index_goster) { ?>
            <article class="list-product mb-30px">
                <div class="img-block">
                    <a href="single-product.html" class="thumbnail">
                        <img class="first-img" src="images/yenigelenurunekle/<?php echo $yenigelenurunekle_index_goster['yenigelenurunekle_resim']; ?>" alt="" />
                    </a>
                    <div class="quick-view">
                        <a class="quick_view" href="#" data-link-action="quickview" title="Quick view" data-bs-toggle="modal" data-bs-target="#exampleModal">
                            <i class="ion-ios-search-strong"></i>
                        </a>
                    </div>
                </div>
                <ul class="product-flag">
                    <li class="new">New</li>
                </ul>
                <div class="product-decs">
                    <a class="inner-link" href="shop-4-column.html"><span>STUDIO DESIGN</span></a>
                    <h2><a href="single-product.html" class="product-link"><?php echo $yenigelenurunekle_index_goster['yenigelenurunekle_baslik']; ?></a></h2>
                    <div class="rating-product">
                        <i class="ion-android-star"></i>
                        <i class="ion-android-star"></i>
                        <i class="ion-android-star"></i>
                        <i class="ion-android-star"></i>
                        <i class="ion-android-star"></i>
                    </div>
                    <div class="pricing-meta">
                        <ul>
                            <li class="old-price">€23.90</li>
                            <li class="current-price">€21.51</li>
                            <li class="discount-price">-10%</li>
                        </ul>
                    </div>
                </div>
                <div class="add-to-link">
                    <ul>
                        <li class="cart"><a class="cart-btn" href="#">ADD TO CART </a></li>
                        <li>
                            <a href="wishlist.html"><i class="ion-android-favorite-outline"></i></a>
                        </li>
                        <li>
                            <a href="compare.html"><i class="ion-ios-shuffle-strong"></i></a>
                        </li>
                    </ul>
                </div>
            </article>

        <?php } ?>

    </div>
</div>

.gridsistemi {
    display: grid;
    grid-template-columns: 100% 100% 100% 100%;
    grid-template-rows: auto auto;
    justify-content: space-between;
    column-gap: 10%;
}