Use most appropriate function for checking URL

From the http.Get() documentation:

> Caller should close resp.Body when done reading from it.

This was not done previously. Since the body is not needed, http.Head() is more appropriate for this application and it
does not impose the requirement to add additional code to clean up.

internal/rule/rulefunction/library.go

@@ -1011,7 +1011,7 @@ func LibraryPropertiesUrlFieldDeadLink() (result ruleresult.Type, output string)
 	}
 
 	logrus.Tracef("Checking URL: %s", url)
-	httpResponse, err := http.Get(url)
+	httpResponse, err := http.Head(url)
 	if err != nil {
 		return ruleresult.Fail, err.Error()
 	}

internal/rule/rulefunction/library_test.go

@@ -751,7 +751,7 @@ func TestLibraryPropertiesUrlFieldDeadLink(t *testing.T) {
 	testTables := []libraryRuleFunctionTestTable{
 		{"Unable to load", "InvalidLibraryProperties", ruleresult.NotRun, ""},
 		{"Not defined", "MissingFields", ruleresult.NotRun, ""},
-		{"Bad URL", "BadURL", ruleresult.Fail, "^Get \"http://invalid/\": dial tcp: lookup invalid:"},
+		{"Bad URL", "BadURL", ruleresult.Fail, "^Head \"http://invalid/\": dial tcp: lookup invalid:"},
 		{"HTTP error 404", "URL404", ruleresult.Fail, "^404 Not Found$"},
 		{"Good URL", "Recursive", ruleresult.Pass, ""},
 	}