tests: use %TESTNUMBER instead of fixed number

This makes the tests easier to copy and relocate to other test numbers
without having to update content.

Closes #6738

tests/data/test24

@@ -25,14 +25,14 @@ http
 HTTP GET fail silently on HTTP error return
  </name>
  <command>
-http://%HOSTIP:%HTTPPORT/24 --fail --silent --show-error
+http://%HOSTIP:%HTTPPORT/%TESTNUMBER --fail --silent --show-error
 </command>
 </client>
 
 # Verify data after the test has been "shot"
 <verify>
 <protocol>
-GET /24 HTTP/1.1
+GET /%TESTNUMBER HTTP/1.1
 Host: %HOSTIP:%HTTPPORT
 User-Agent: curl/%VERSION
 Accept: */*
@@ -41,7 +41,7 @@ Accept: */*
 <errorcode>
 22
 </errorcode>
-<file2 name="log/stderr24" mode="text">
+<file2 name="log/stderr%TESTNUMBER" mode="text">
 curl: (22) The requested URL returned error: 404
 </file2>
 </verify>