build: improve patch filename remembering

[nornagon]

Description of Change

This improves the quality of the system that handles remembering what filenames patches have. Previously, it would forget the filename of a patch if a stat block was included, e.g.

From 069f545fb7e14ad7149cdeea9865eeb76972fa48 Mon Sep 17 00:00:00 2001
From: Jeremy Apthorp <nornagon@nornagon.net>
Date: Thu, 9 Apr 2020 16:58:34 -0700
Subject: [PATCH] build: improve patch filename remembering

---
 script/lib/patches.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/script/lib/patches.py b/script/lib/patches.py
index c3035b88e..2365303de 100644
--- a/script/lib/patches.py
+++ b/script/lib/patches.py
@@ -8,11 +8,13 @@ def read_patch(patch_dir, patch_filename):
[...]

because it would add the Patch-Filename information after the --- separator, resulting in the information not being included in the commit message.

This additionally fixes an issue where the Patch-Filename header was being injected into the patch before every diff --git line, instead of only the first.

Checklist

• PR description included and stakeholders cc'd
• PR title follows semantic commit guidelines

Release Notes

Notes: none

[jkleinsc]

Merging as CI failures unrelated to PR change.

[release-clerk]

No Release Notes

[trop]

I was unable to backport this PR to "6-1-x" cleanly;
you will need to perform this backport manually.

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I was unable to backport this PR to "7-2-x" cleanly;
you will need to perform this backport manually.

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I have automatically backported this PR to "9-x-y", please check out #23092

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I have automatically backported this PR to "8-x-y", please check out #23093

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@nornagon has manually backported this PR to "7-2-x", please check out #23184

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@nornagon has manually backported this PR to "6-1-x", please check out #23185