Fix testSelfUpperBoundInference test in LV 2.0 branch

The test starts failing after switching to 2.0 because we don't support
TypeInferenceOnCallsWithSelfTypes though it's planned (see KT-59012).

This particular test was introduced in 1.5.x (see KT-48026) to check
if the flag -Xself-upper-bound-inference actually enables
the feature TypeInferenceOnCallsWithSelfTypes.

While the feature is enabled by default since 1.6, it doesn't make sense
to have it with earlier versions.
Another solution would be removing it at all, but that might require
removing related code as well (as we would have some dead code in CLI
arguments processing).

^KT-60885 Fixed

compiler/testData/cli/jvm/selfUpperBoundInference.args

@@ -1,4 +1,6 @@
 $TESTDATA_DIR$/selfUpperBoundInference.kt
 -d
 $TEMP_DIR$
+-language-version
+1.5
 -Xself-upper-bound-inference

compiler/testData/cli/jvm/selfUpperBoundInference.out

@@ -1,3 +1,4 @@
+warning: language version 1.5 is deprecated and its support will be removed in a future version of Kotlin
 compiler/testData/cli/jvm/selfUpperBoundInference.kt:40:25: warning: unchecked cast: WriterAppender.Builder1<B> to B
             return this as B
                         ^