Added test file for the issue

Author: EbinJose2002

flang/test/Lower/adjustr.f90

@@ -0,0 +1,14 @@
+! RUN: bbc -emit-fir -o - %s | FileCheck %s
+
+! Checking no reference to boxchar conversion is in the emitted fir.
+! CHECK-NOT: (!fir.ref<!fir.char<1,4>>) -> !fir.boxchar<1>
+
+program main
+  logical         ,dimension(1):: mask = .true.
+  character(len=2),dimension(1):: d1 = "a "
+  character(len=4),dimension(1):: d4
+  where (mask)
+    d4 = adjustr(d1 // d1)
+  end where
+  write(6,*) "d4     =", d4
+end