Adding missing test cases for linsert command (#12040)

Currently LINSERT command does not have the test case coverage for following scenarios.
1. When key does not exist, it is considered an empty list and no operation is performed.
2. An error is returned when key exists but does not hold a list value.

Added above two missing test cases for linsert command.

tests/unit/type/list.tcl

@@ -1416,6 +1416,15 @@ foreach {pop} {BLPOP BLMPOP_LEFT} {
         set e
     } {*ERR*syntax*error*}
 
+    test {LINSERT against non-list value error} {
+        r set k1 v1
+        assert_error {WRONGTYPE Operation against a key holding the wrong kind of value*} {r linsert k1 after 0 0}
+    }
+
+    test {LINSERT against non existing key} {
+        assert_equal 0 [r linsert not-a-key before 0 0]
+    }
+
 foreach type {listpack quicklist} {
     foreach {num} {250 500} {
         if {$type == "quicklist"} {