Fix comparison of tyGenericBody in typerel (#8045)

As shown in #7734 and #7733 the logic in typerel fails to determine that
`type Foo` and `type Foo` are indeed equal.

Fixes #7734

compiler/sigmatch.nim

@@ -1425,7 +1425,7 @@ proc typeRelImpl(c: var TCandidate, f, aOrig: PType,
 
   of tyGenericBody:
     considerPreviousT:
-      if a.kind == tyGenericInst and a.sons[0] == f:
+      if a == f or a.kind == tyGenericInst and a.sons[0] == f:
         bindingRet isGeneric
       let ff = lastSon(f)
       if ff != nil:

tests/typerel/t7734.nim

@@ -0,0 +1,19 @@
+type
+  Foo[T: SomeFloat] = object
+    learning_rate: T
+
+  Bar[T: SomeFloat] = object
+    learning_rate: T
+    momentum: T
+
+  Model = object
+    weight: int
+
+  FooClass = Foo or Bar
+
+
+proc optimizer[M; T: SomeFloat](model: M, _: typedesc[Foo], learning_rate: T): Foo[T] =
+  result.learning_rate = learning_rate
+
+let a = Model(weight: 1)
+let opt = a.optimizer(Foo, 10.0)