flatpak: Fix gmime build

Apparently it does a explicit version check for automake, but in such a
way that it needs to be patched on new automake versions. Patch this out
while we await the PR upstream to be merged into master.

See: https://github.com/jstedfast/gmime/pull/180

build-aux/patches/gmime-autogen.sh-Also-allow-automake-1.18.patch

@@ -0,0 +1,25 @@
+From 22bb4d88a62924ceaf358e5c9871dbe05ae3464c Mon Sep 17 00:00:00 2001
+From: Niels De Graef <ndegraef@redhat.com>
+Date: Mon, 24 Nov 2025 00:38:22 +0100
+Subject: [PATCH] autogen.sh: Also allow automake 1.18
+
+---
+ autogen.sh | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/autogen.sh b/autogen.sh
+index af13973f..8dc5437e 100755
+--- a/autogen.sh
++++ b/autogen.sh
+@@ -57,7 +57,7 @@ fi
+ 	DIE=1
+ }
+ 
+-for automake_version in 1.9 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17; do
++for automake_version in 1.9 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18; do
+     if automake-${automake_version} --version < /dev/null > /dev/null 2>&1 ; then
+         AUTOMAKE=automake-${automake_version}
+         ACLOCAL=aclocal-${automake_version}
+-- 
+2.51.1
+

org.gnome.Geary.json

@@ -211,6 +211,12 @@
                     "type": "git",
                     "url": "https://github.com/jstedfast/gmime.git",
                     "branch": "master"
+                },
+                {
+                    "type": "patch",
+                    "paths": [
+                        "build-aux/patches/gmime-autogen.sh-Also-allow-automake-1.18.patch"
+                    ]
                 }
             ]
         },