Add operator==(Quotient::Tag, Quotient::Tag)

operator==() is not synthesized from non-defaulted operator<=>(), see
https://en.cppreference.com/w/cpp/language/default_comparisons#Implicit_declaration

Quotient/events/accountdataevents.h

@@ -14,7 +14,7 @@ constexpr inline auto ServerNoticeTag = "m.server_notice"_L1;
 
 using TagRecord [[deprecated("Use Tag from csapi/definitions/tag.h instead")]] = Tag;
 
-inline std::partial_ordering operator<=>( //
+inline std::partial_ordering operator<=>(
     const Tag& lhs, const Tag& rhs) // clazy:exclude=function-args-by-value
 {
     // Per The Spec, rooms with no order should be after those with order,
@@ -24,6 +24,11 @@ inline std::partial_ordering operator<=>( //
                                        : *lhs.order <=> *rhs.order;
 }
 
+inline bool operator==(const Tag& lhs, const Tag& rhs) // clazy:exclude=function-args-by-value
+{
+    return std::is_eq(lhs <=> rhs);
+}
+
 using TagsMap = QHash<QString, Tag>;
 
 DEFINE_SIMPLE_EVENT(TagEvent, Event, "m.tag", TagsMap, tags, "tags")