[dvsim] Fix testplan bugs

- Milestone regressions broken - #6686
- Coverage documentation is not properly formatted

Signed-off-by: Srikrishna Iyer <sriyer@google.com>
diff --git a/util/dvsim/Testplan.py b/util/dvsim/Testplan.py
index d9d2246..d9c2488 100644
--- a/util/dvsim/Testplan.py
+++ b/util/dvsim/Testplan.py
@@ -347,7 +347,7 @@
         regressions = defaultdict(set)
         for tp in self.testpoints:
             if tp.milestone in tp.milestones[1:]:
-                regressions[tp.milestone].union({t for t in tp.tests if t})
+                regressions[tp.milestone].update({t for t in tp.tests if t})
 
         # Build regressions dict into a hjson like data structure
         return [{
@@ -390,7 +390,7 @@
             colalign = ("center", "left")
             table = []
             for covergroup in self.covergroups:
-                desc = covergroup.desc.strip()
+                desc = _fmt_text(covergroup.desc.strip(), fmt)
                 table.append([covergroup.name, desc])
             lines += [
                 tabulate(table,