[common, yuzu] Fix compilation on newer httplib versions (#4278)

Required for newer httplib versions to compile.

has_header is at least present on 0.38.0 on my local machine. Let's hope
it works on Trixie

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

- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md)
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.

-------------------

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4278
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Reviewed-by: Samuel <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.has_header("content-type")) {
             LOG_ERROR(Common, "GET to {}{} returned no content", url, path);
             return {};
         }

src/yuzu/updater/update_dialog.cpp

@@ -74,6 +74,7 @@ UpdateDialog::~UpdateDialog() {
     delete ui;
 }
 
+// TODO: migrate to a net.cpp wrapper
 void UpdateDialog::Download() {
     const auto filename = QtCommon::Frontend::GetSaveFileName(
         tr("New Version Location"),
@@ -161,7 +162,7 @@ void UpdateDialog::Download() {
                                               QString::number(response.status)));
         return;
     }
-    if (!response.headers.contains("content-type")) {
+    if (!response.has_header("content-type")) {
         LOG_ERROR(Frontend, "GET to {}{} returned no content", m_asset.url, m_asset.path);
         return;
     }