Fix incorrect warning on type ascription for backquoted identifiers in patterns

Author: nox213

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -3177,7 +3177,7 @@ object Parsers {
     def pattern1(location: Location = Location.InPattern): Tree =
       val p = pattern2(location)
       if in.isColon then
-        val isVariableOrNumber = isVarPattern(p) || p.isInstanceOf[Number]
+        val isVariableOrNumber = isVarPattern(p) || p.isInstanceOf[Number] || isBackquoted(p)
         if !isVariableOrNumber then
           report.errorOrMigrationWarning(
             em"""Type ascriptions after patterns other than:

tests/pos/i15784.scala

@@ -2,7 +2,4 @@ def i15784 = List(42) match
   case List(_, rest @ _*) => rest
   case List(_, Rest @ _*) => Rest
   case List(_, `Rest` @ _*) => Rest
-  case _ => ???
-
-def i15784_auxiliary = 42 match
-  case `type` : Int => `type`
+  case _ => ???

tests/pos/i22989.scala

@@ -0,0 +1,3 @@
+//> using options -Xfatal-warnings
+def foo = 42 match
+  case `type` : Int => `type`