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

We exclude testData pattern from copyright scope

analysis/low-level-api-fir/testData/getOrBuildFirBinary/topLevelFunction.txt

@@ -0,0 +1,8 @@
+KT element: KtNamedFunction
+KT element text:
+public fun doSmth(): kotlin.Unit { /* compiled code */ }
+FIR element: FirSimpleFunctionImpl
+FIR source kind: KtRealSourceElementKind
+
+FIR element rendered:
+public final [ResolvedTo(BODY_RESOLVE)] fun doSmth(): R|kotlin/Unit|