Fix server crash when header with only digits in name sended

Author: luzrain

psalm.xml

@@ -27,5 +27,10 @@
                 <directory name="src" />
             </errorLevel>
         </PropertyNotSetInConstructor>
+        <RedundantCastGivenDocblockType>
+            <errorLevel type="suppress">
+                <directory name="src" />
+            </errorLevel>
+        </RedundantCastGivenDocblockType>
     </issueHandlers>
 </psalm>

src/Server/Http/Psr7/MessageTrait.php

@@ -141,14 +141,14 @@ public function withBody(StreamInterface $body): MessageInterface
     private function setHeaders(array $headers): void
     {
         foreach ($headers as $name => $value) {
-            $normalizedName = $this->normalizeHeaderName($name);
-            $value = $this->normalizeHeaderValue($value);
+            $normalizedName = $this->normalizeHeaderName((string) $name);
+            $valuse = $this->normalizeHeaderValue($value);
             if (isset($this->headerNames[$normalizedName])) {
                 $name = $this->headerNames[$normalizedName];
-                $this->headers[$name] = \array_merge($this->headers[$name], $value);
+                $this->headers[$name] = \array_merge($this->headers[$name], $valuse);
             } else {
                 $this->headerNames[$normalizedName] = $name;
-                $this->headers[$name] = $value;
+                $this->headers[$name] = $valuse;
             }
         }
     }