为什么我的HTML表单试图执行PHP但是index.html中没有PHP？

Question

   <div class="row contact__main">
        <div class="col-eight tab-full contact__form">
            <form name="contactForm" id="contactForm" method="post" action="https://formspree.io/censored@gmail.com">
                <fieldset>

                <div class="form-field">
                    <input name="contactName" type="text" id="contactName" placeholder="Name" value="" minlength="2" required="" aria-required="true" class="full-width">
                </div>
                <div class="form-field">
                    <input name="contactEmail" type="email" id="contactEmail" placeholder="Email" value="" required="" aria-required="true" class="full-width">
                </div>
                <div class="form-field">
                    <input name="contactSubject" type="text" id="contactSubject" placeholder="Subject" value="" class="full-width">
                </div>
                <div class="form-field">
                    <textarea name="contactMessage" id="contactMessage" placeholder="message" rows="10" cols="50" required="" aria-required="true" class="full-width"></textarea>
                </div>
                <div class="form-field">
                    <button class="full-width btn--primary">Submit</button>
                    <div class="submit-loader">
                        <div class="text-loader">Sending...</div>
                        <div class="s-loader">
                            <div class="bounce1"></div>
                            <div class="bounce2"></div>
                            <div class="bounce3"></div>
                        </div>
                    </div>
                </div>

                </fieldset>
            </form>

            <!-- contact-warning -->
            <div class="message-warning">
                Something went wrong. Please try again.
            </div> 

            <!-- contact-success -->
            <div class="message-success">
                Your message was sent, thank you!<br>
            </div>

这是我的网站：https://xpmai.tumblr.com/test

根据我在Chrome浏览器控制台中看到的内容，该表单尝试从GitHub执行PHP，但GitHub不支持PHP。所以它失败了。但奇怪的是，它只是一种HTML形式。整个 index.html 没有一个PHP代码。那我怎么解决这个问题呢？

编辑：为了更具体和简单，我有一个HTML表单。当我尝试提交表单时，它说PHP错误。 jquery-3.2.1.min.js:4 POST https://xpmai.tumblr.com/inc/sendEmail.php 404 ()但是在上面的代码中，我无法弄清楚如何解决它。如何禁用PHP并使其执行上面的 POST 操作？