Fix tests not passing for vim

Vim introduced more accurate profiling accuracy in commit
076de79ad832558267b3ff903c048df2f4c1a5d6 [0], which increases the
precision down to nanosecond precision.

However this collides with printf("%f") accuracy, which starts rounding
floating point numbers much earlier. Since we compare the evaluated
string with the real value retrieved from the benchmarking log file, we
get an error if they don't match perfectly.

Arguably that comparison is a bit too strict anyway, but luckily we can
just set the precision for printf() by adding a ".x" prefix.

This makes the tests pass again.

[0] vim/vim#12129

Author: vimpostor

tests/test_general.vim

@@ -145,10 +145,10 @@ func Test_performance()
 	call assert_equal(printf("Called %d times", call_num), log[2])
 
 	let total_time = str2float(log[3]->matchstr('\d\.\d\+'))
-	call assert_equal(printf("Total time:   %f", total_time), log[3])
+	call assert_equal(printf("Total time:   %.9f", total_time), log[3])
 
 	let self_time = str2float(log[4]->matchstr('\d\.\d\+'))
-	call assert_equal(printf(" Self time:   %f", self_time), log[4])
+	call assert_equal(printf(" Self time:   %.9f", self_time), log[4])
 
 	let individual_time = total_time / call_num
 	echo printf("Called %d times\nTotal time: %f\n Self time: %f\nIndividual time: %f", call_num, total_time, self_time, individual_time)