EPA: Preserve comments for pattern synonym sig

Closes #24749

compiler/GHC/Parser.y

@@ -2653,7 +2653,7 @@ sigdecl :: { LHsDecl GhcPs }
                                     (Fixity fixText fixPrec (unLoc $1)))))
                    }}
 
-        | pattern_synonym_sig   { sL1a $1 . SigD noExtField . unLoc $ $1 }
+        | pattern_synonym_sig   { L (getLoc $1) . SigD noExtField . unLoc $ $1 }
 
         | '{-# COMPLETE' qcon_list opt_tyconsig  '#-}'
                 {% let (dcolon, tc) = $3

testsuite/tests/printer/Makefile

@@ -846,3 +846,8 @@ Test24748:
 DataDeclShort:
 	$(CHECK_PPR)   $(LIBDIR) DataDeclShort.hs
 	$(CHECK_EXACT) $(LIBDIR) DataDeclShort.hs
+
+.PHONY: Test24749
+Test24749:
+	$(CHECK_PPR)   $(LIBDIR) Test24749.hs
+	$(CHECK_EXACT) $(LIBDIR) Test24749.hs

testsuite/tests/printer/Test24749.hs

+{-# LANGUAGE PatternSynonyms #-}
+module Test24749 where
+
+-- c0
+pattern (:|) ::
+  -- c1
+  a ->
+  -- c2
+  a ->
+  -- c3
+  Domino a

testsuite/tests/printer/all.T

@@ -202,3 +202,4 @@ test('CaseAltComments', [ignore_stderr, req_ppr_deps], makefile_test, ['CaseAltC
 test('MatchPatComments', [ignore_stderr, req_ppr_deps], makefile_test, ['MatchPatComments'])
 test('Test24748', [ignore_stderr, req_ppr_deps], makefile_test, ['Test24748'])
 test('DataDeclShort', [ignore_stderr, req_ppr_deps], makefile_test, ['DataDeclShort'])
+test('Test24749', [ignore_stderr, req_ppr_deps], makefile_test, ['Test24749'])