time_format: Determine year difference based on months passed (#47687)

The inline git blame always calculated the difference in years for
commits based solely upon the difference between the years and not
actual time passed. This is currently somewhat unfortunate during
January, as for all dates starting from 2024 and lower, we would show `2
years ago`, even if the date was the 31st of December 2024.

This fixes/improves this to use the lower bound always instead, as I
find this much more intuitive - we can probably look into even better
formatting here at some other point.

Release Notes:

- Fixed an issue where relative time deltas would sometimes show as `n +
1 years` instead of the actual `n years`.

crates/time_format/src/time_format.rs

@@ -257,13 +257,11 @@ fn format_relative_date(timestamp: OffsetDateTime, reference: OffsetDateTime) ->
                     match month_diff {
                         0..=1 => "1 month ago".to_string(),
                         2..=11 => format!("{} months ago", month_diff),
-                        _ => {
-                            let timestamp_year = timestamp_date.year();
-                            let reference_year = reference_date.year();
-                            let years = reference_year - timestamp_year;
+                        months => {
+                            let years = months / 12;
                             match years {
                                 1 => "1 year ago".to_string(),
-                                _ => format!("{} years ago", years),
+                                _ => format!("{years} years ago"),
                             }
                         }
                     }
@@ -910,6 +908,65 @@ mod tests {
         assert_eq!(format_relative_date(next_month(), reference), "1 year ago");
     }
 
+    #[test]
+    fn test_relative_format_years() {
+        let reference = create_offset_datetime(1990, 4, 12, 23, 0, 0);
+
+        // 12 months
+        assert_eq!(
+            format_relative_date(create_offset_datetime(1989, 4, 12, 23, 0, 0), reference),
+            "1 year ago"
+        );
+
+        // 13 months
+        assert_eq!(
+            format_relative_date(create_offset_datetime(1989, 3, 12, 23, 0, 0), reference),
+            "1 year ago"
+        );
+
+        // 23 months
+        assert_eq!(
+            format_relative_date(create_offset_datetime(1988, 5, 12, 23, 0, 0), reference),
+            "1 year ago"
+        );
+
+        // 24 months
+        assert_eq!(
+            format_relative_date(create_offset_datetime(1988, 4, 12, 23, 0, 0), reference),
+            "2 years ago"
+        );
+
+        // 25 months
+        assert_eq!(
+            format_relative_date(create_offset_datetime(1988, 3, 12, 23, 0, 0), reference),
+            "2 years ago"
+        );
+
+        // 35 months
+        assert_eq!(
+            format_relative_date(create_offset_datetime(1987, 5, 12, 23, 0, 0), reference),
+            "2 years ago"
+        );
+
+        // 36 months
+        assert_eq!(
+            format_relative_date(create_offset_datetime(1987, 4, 12, 23, 0, 0), reference),
+            "3 years ago"
+        );
+
+        // 37 months
+        assert_eq!(
+            format_relative_date(create_offset_datetime(1987, 3, 12, 23, 0, 0), reference),
+            "3 years ago"
+        );
+
+        // 120 months
+        assert_eq!(
+            format_relative_date(create_offset_datetime(1980, 4, 12, 23, 0, 0), reference),
+            "10 years ago"
+        );
+    }
+
     #[test]
     fn test_calculate_month_difference() {
         let reference = create_offset_datetime(1990, 4, 12, 23, 0, 0);