remove unnecessary interpolation (apache#578)

Author: pjfanning

http-core/src/main/scala/org/apache/pekko/http/scaladsl/model/HttpHeader.scala

@@ -103,9 +103,9 @@ object HttpHeader {
             case e: ParseError => parser.parseError(e)
             case e             => parser.failure(e)
           }).info
-          ParsingResult.Error(info.withSummaryPrepended(s"Illegal HTTP header value"))
+          ParsingResult.Error(info.withSummaryPrepended("Illegal HTTP header value"))
       }
-    } else ParsingResult.Error(ErrorInfo(s"Illegal HTTP header name", name))
+    } else ParsingResult.Error(ErrorInfo("Illegal HTTP header name", name))
 
   /** INTERNAL API */
   @InternalApi

http-core/src/test/scala/org/apache/pekko/http/impl/model/parser/HttpHeaderSpec.scala

@@ -877,7 +877,7 @@ class HttpHeaderSpec extends AnyFreeSpec with Matchers {
       ErrorInfo("Illegal HTTP header 'User-Agent': Illegal header value", "Header comment nested too deeply")
     }
 
-    "should not broken when header-value is null" in {
+    "not break when header-value is null" in {
       val errors = parse("Content-Disposition", null).errors
       errors should have size 1
       errors.head shouldBe an[ErrorInfo]