test1908: avoid using fixed port number in test data

Closes #5225
diff --git a/tests/data/test1908 b/tests/data/test1908
index de34d0e..236bd4a 100644
--- a/tests/data/test1908
+++ b/tests/data/test1908
@@ -65,7 +65,7 @@
 <file name="log/altsvc-1908">
 # Your alt-svc cache. https://curl.haxx.se/docs/alt-svc.html
 # This file was generated by libcurl! Edit at your own risk.
-h1 127.0.0.1 8990 h2 3dbbdetxoyw4nsp6c3cc456oj2ays6s43ezxzsfxxri3h5xqd.example 443 TIMESTAMP 1 0
+h1 127.0.0.1 %HTTPPORT h2 3dbbdetxoyw4nsp6c3cc456oj2ays6s43ezxzsfxxri3h5xqd.example 443 TIMESTAMP 1 0
 </file>
 </verify>
 </testcase>