Hello,
there is a method str1.equalsIgnoreCase(str2) which may be suitable for you. But you have to change your code a little bit. Look at my POC code:
RequestObject ro = new RestRequestObjectBuilder()
.withRestUrl("https://jsonplaceholder.typicode.com/users")
.withRestRequestMethod("GET")
.build()
ResponseObject resp = WS.sendRequest(ro)
def parsedResp = new JsonSlurper().parseText(resp.getResponseText())
String getProperty = parsedResp.name[0]
String caseInsensitiveProperty = "leAnNE grAHaM"
assert getProperty.equalsIgnoreCase(caseInsensitiveProperty)
Just change your variables and it should work.