testsuite: XFAIL gfortran.dg/initialization_25.f90 properly

The test was disabled/XFAIL'd informally in r0-100012-gcdc6637d7c78ec,
but r15-3890-g34bf6aa41ba539 didn't realize this, causing a FAIL.

Fix that by marking it as XFAIL per the original intent.

gcc/testsuite/ChangeLog:
	PR fortran/35779
	PR fortran/116858

	* gfortran.dg/initialization_25.f90: Mark as XFAIL.

gcc/testsuite/gfortran.dg/initialization_25.f90

@@ -5,8 +5,8 @@
 ! Dick Hendrickson <dick DOT hendrickson AT gmail DOT com>
 !
 ! Initial patch was reverted as it broke nested loops (see initialization_26.f90).
-!
+! XFAIL is for PR35779
 
 !   INTEGER :: J1
-!   INTEGER,PARAMETER :: I2(10) = (/(J1,J1=its_bad,1,-1)/) ! { dg-error "does not reduce" }
+!   INTEGER,PARAMETER :: I2(10) = (/(J1,J1=its_bad,1,-1)/) ! { dg-error "does not reduce" { xfail *-*-* } }
 END