patch 8.2.1697: inconsistent capitalization of error messages

Problem:    Inconsistent capitalization of error messages.
Solution:   Always start with a capital.
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index bb2bfaf..c400e82 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -1974,7 +1974,7 @@
     source Ximport.vim
   catch /E1001/
     # Error should be fore the Xexported.vim file.
-    assert_match('E1001: variable not found: notDefined', v:exception)
+    assert_match('E1001: Variable not found: notDefined', v:exception)
     assert_match('function <SNR>\d\+_ImpFunc\[1\]..<SNR>\d\+_ExpFunc, line 1', v:throwpoint)
   endtry