Update irbuild-str.test

Author: BobTheBuidler

mypyc/test-data/irbuild-str.test

@@ -605,3 +605,19 @@ L3:
     r6 = r7
 L4:
     return r6
+
+[case testFStringFromConstants]
+from typing import Final
+string: Final = "abc"
+integer: Final = 123
+floating: Final = 3.14
+
+def test(x: str) -> str:
+    return f"{string}{integer}{floating}{x}"
+
+[out]
+def test(x):
+    x, r0 :: str
+
+L0:
+   'abc1233.14 '