[LL FIR] rename testdata to testData to avoid copyright generation

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/getOrBuildFirBinary/publishedApi/publishedApiPropertySetter.txt

@@ -0,0 +1,8 @@
+KT element: KtPropertyAccessor
+KT element text:
+internal final set(value: kotlin.String) {/* compiled code */ }
+FIR element: FirPropertyAccessorImpl
+FIR source kind: KtRealSourceElementKind
+
+FIR element rendered:
+internal [ResolvedTo(BODY_RESOLVE)] [LazyPublishedApiEffectiveVisibilityKey=public] set([ResolvedTo(BODY_RESOLVE)] value: R|kotlin/String|): R|kotlin/Unit|