refactoring: tangent function test, rename

src/test/test_funktionen.c

@@ -149,7 +149,7 @@ void test_cosine_for_1(void) {
     // Add more test cases for different inputs and expected outputs
 }
 
-void test_tangent(void) {
+void test_tangent_for_1_5(void) {
     float result = tangent(1.5);
     TEST_ASSERT_EQUAL_FLOAT(14.101419, result);
     // Add more test cases for different inputs and expected outputs