[PATCH 4/4] Switch remaining Message-Id headers to Message-ID

[Kyle Meyer <kyle@kyleam.com>]

The two previous commits updated the piem-add-message-id-header
functionality for git.git's change from Message-Id to Message-ID.
Updates a couple of remaining spots to use Message-ID for consistency.
---
 piem.el                   | 2 +-
 tests/piem-rmail-tests.el | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/piem.el b/piem.el
index 01985f0e..abc87b10 100644
--- a/piem.el
+++ b/piem.el
@@ -759,7 +759,7 @@ (defun piem--write-mbox-to-maildir (maildir-directory)
                                      (save-excursion
                                        (message-narrow-to-head-1)
                                        (message-fetch-field "message-id" t)))
-                                   (error "Message lacks Message-Id header")))))))
+                                   (error "Message lacks Message-ID header")))))))
             (cl-incf n-skipped)
           (let ((case-fold-search nil))
             (while (re-search-forward
diff --git a/tests/piem-rmail-tests.el b/tests/piem-rmail-tests.el
index f56e2f26..7ee0a553 100644
--- a/tests/piem-rmail-tests.el
+++ b/tests/piem-rmail-tests.el
@@ -38,7 +38,7 @@ (defvar piem-rmail-tests-mbox-text "\
 Cc: i@inbox.example.com
 Subject: Re: test
 Date: Sun, 23 May 2021 02:26:51 -0400
-Message-Id: <456@example.com>
+Message-ID: <456@example.com>
 In-Reply-To: <123@example.com>
 References: <123@example.com>
 
-- 
2.39.2