patch 9.1.1065: no digraph for "Approaches the limit"

Problem:  no digraph for "Approaches the limit"
Solution: Add the digraph using .= (Hans Ginzel)

Add digraph Approaches the Limit

≐ U+2250 https://www.fileformat.info/info/unicode/char/2250/index.htm

closes: #16508

Signed-off-by: Hans Ginzel <hans@matfyz.cz>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_digraph.vim b/src/testdir/test_digraph.vim
index 88b8ded..29fa300 100644
--- a/src/testdir/test_digraph.vim
+++ b/src/testdir/test_digraph.vim
@@ -40,6 +40,9 @@
   " Quadruple prime
   call Put_Dig("'4")
   call assert_equal("⁗", getline('.'))
+  " APPROACHES THE LIMIT
+  call Put_Dig(".=")
+  call assert_equal("≐", getline('.'))
   " Not a digraph
   call Put_Dig("a\<bs>")
   call Put_Dig("\<bs>a")