[common/net] fix build errors on Arch with cpp-httplib 0.52x

Signed-off-by: lizzie <lizzie@eden-emu.dev>

src/common/net/net.cpp

@@ -241,7 +241,7 @@ std::optional<std::string> MakeRequest(const std::string& url, const std::string
                       response.status);
             return {};
         }
-        if (!response.headers.contains("content-type")) {
+        if (response.headers.find("content-type") == response.headers.end()) {
             LOG_ERROR(Common, "GET to {}{} returned no content", url, path);
             return {};
         }

src/yuzu/updater/update_dialog.cpp

@@ -161,7 +161,7 @@ void UpdateDialog::Download() {
                                               QString::number(response.status)));
         return;
     }
-    if (!response.headers.contains("content-type")) {
+    if (response.headers.find("content-type") == response.headers.end()) {
         LOG_ERROR(Frontend, "GET to {}{} returned no content", m_asset.url, m_asset.path);
         return;
     }