BackendOptionsProxyTest2 fails on JDK 17 (and 20)

[SethTisue]

on JDK 11, it passes

this came up in the Scala 2.13 community build

[info] welcome to sbt 1.8.2 (Eclipse Adoptium Java 17.0.6)
...
sbt:sttp> core/testOnly *BackendOptionsProxyTest2
...
[info] BackendOptionsProxyTest2:
[info] - should throw UnsupportedOperationException with reason *** FAILED *** (7 milliseconds)
[info]   "... fakeproxyserverhost[/<unresolved>]:8080" was not equal to "... fakeproxyserverhost[]:8080" (BackendOptionsProxyTest2.scala:25)
[info]   Analysis:
[info]   "... fakeproxyserverhost[/<unresolved>]:8080" -> "... fakeproxyserverhost[]:8080"