Fix touch -t with 2 digit years when YY > 68

When using `touch -t` with a 2 digit year, the year is interpreted as
a relative year to 2000.

When the year is 68 or less, it should be interpreted as 20xx.
When the year is 69 or more, it should be interpreted as 19xx.

This is the behavior of GNU `touch`.

fixes gh-7280

Arguably 2 digits years should be deprecated as we
are already closer to 2069, than 1969.

tests/by-util/test_touch.rs

@@ -118,6 +118,45 @@ fn test_touch_set_mdhms_time() {
     assert_eq!(mtime.unix_seconds() - start_of_year.unix_seconds(), 45296);
 }
 
+#[test]
+fn test_touch_2_digit_years_68() {
+    // 68 and before are 20xx
+    let (at, mut ucmd) = at_and_ucmd!();
+    let file = "test_touch_set_two_digit_68_time";
+
+    ucmd.args(&["-t", "6801010000", file])
+        .succeeds()
+        .no_output();
+
+    assert!(at.file_exists(file));
+
+    //  January 1, 2068, 00:00:00
+    let expected = FileTime::from_unix_time(3_092_601_600, 0);
+    let (atime, mtime) = get_file_times(&at, file);
+    assert_eq!(atime, mtime);
+    assert_eq!(atime, expected);
+    assert_eq!(mtime, expected);
+}
+
+#[test]
+fn test_touch_2_digit_years_69() {
+    // 69 and after are 19xx
+    let (at, mut ucmd) = at_and_ucmd!();
+    let file = "test_touch_set_two_digit_69_time";
+
+    ucmd.args(&["-t", "6901010000", file])
+        .succeeds()
+        .no_output();
+
+    assert!(at.file_exists(file));
+    // January 1, 1969, 00:00:00
+    let expected = FileTime::from_unix_time(-31_536_000, 0);
+    let (atime, mtime) = get_file_times(&at, file);
+    assert_eq!(atime, mtime);
+    assert_eq!(atime, expected);
+    assert_eq!(mtime, expected);
+}
+
 #[test]
 fn test_touch_set_ymdhm_time() {
     let (at, mut ucmd) = at_and_ucmd!();