FIR: apply minor test data fixes around type mismatch problems

compiler/fir/analysis-tests/testData/resolveWithStdlib/contracts/fromSource/good/returnsImplies/eqNotEq.fir.txt

@@ -1,5 +1,5 @@
 FILE: eqNotEq.kt
-    public final fun checkNotNull(x: R|kotlin/Any?|): R|kotlin/Unit|
+    public final fun checkNotNull(x: R|kotlin/Any?|): R|kotlin/Boolean|
         [R|Contract description]
          <
             Returns(TRUE) -> x != null

compiler/fir/analysis-tests/testData/resolveWithStdlib/contracts/fromSource/good/returnsImplies/eqNotEq.kt

@@ -1,11 +1,11 @@
 import kotlin.contracts.*
 
-fun checkNotNull(x: Any?) {
+fun checkNotNull(x: Any?): Boolean {
     contract {
         returns(true) implies (x != null)
         returns(false) implies (x == null)
     }
-    return <!RETURN_TYPE_MISMATCH!>x != null<!>
+    return x != null
 }
 
 fun trickyRequireNotNull(x: Any?) {

compiler/fir/analysis-tests/testData/resolveWithStdlib/contracts/fromSource/good/returnsImplies/typePredicate.fir.txt

@@ -1,5 +1,5 @@
 FILE: typePredicate.kt
-    public final fun checkIsString(x: R|kotlin/Any|): R|kotlin/Unit|
+    public final fun checkIsString(x: R|kotlin/Any|): R|kotlin/Boolean|
         [R|Contract description]
          <
             Returns(TRUE) -> x is kotlin/String

compiler/fir/analysis-tests/testData/resolveWithStdlib/contracts/fromSource/good/returnsImplies/typePredicate.kt

@@ -1,11 +1,11 @@
 import kotlin.contracts.*
 
-fun checkIsString(x: Any) {
+fun checkIsString(x: Any): Boolean {
     contract {
         returns(true) implies (x is String)
         returns(false) implies (x !is String)
     }
-    return <!RETURN_TYPE_MISMATCH!>x is String<!>
+    return x is String
 }
 
 fun test(x: Any) {