[crater] Work around diffs rounded to 100%

Sometimes ttx_diff reports a diff with ratio of 1.0, and we were
treating this the same as if it was identical. This patch makes sure we
are distinguishing between 'identical' and 'very very close' by manually
nudging the percent in this case.

fontc_crater/src/ci/html.rs

@@ -410,7 +410,12 @@ fn make_diff_report(
                     k,
                     match v {
                         DiffOutput::Identical => 100.0,
-                        DiffOutput::Diffs(d) => d.get("total").unwrap().ratio().unwrap() * 100.0,
+                        DiffOutput::Diffs(d) => {
+                            // sometimes the output is rounded up to 100 but is
+                            // not actually identical: we want to not show that as 100!
+                            let diff_perc = d.get("total").unwrap().ratio().unwrap() * 100.0;
+                            diff_perc.min(99.999)
+                        }
                     },
                 )
             })