Bump libxml2 (#2118)

Also fix rav1e in the docker image after
https://github.com/AOMediaCodec/libavif/pull/2117
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ef09db2..df2ffb8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -58,6 +58,7 @@
 * Update aom.cmd: v3.8.2
 * Update dav1d.cmd: 1.4.1
 * Update libgav1.cmd: v0.19.0
+* Update libxml2.cmd: v2.12.6
 * Update libyuv.cmd: a6a2ec65
 * Update rav1e.cmd: v0.7.1
 * Update svt.cmd/svt.sh: v2.0.0
diff --git a/cmake/Modules/LocalLibXml2.cmake b/cmake/Modules/LocalLibXml2.cmake
index 01cdc84..3ec107d 100644
--- a/cmake/Modules/LocalLibXml2.cmake
+++ b/cmake/Modules/LocalLibXml2.cmake
@@ -1,4 +1,4 @@
-set(AVIF_LOCAL_LIBXML_GIT_TAG "v2.11.5")
+set(AVIF_LOCAL_LIBXML_GIT_TAG "v2.12.6")
 
 set(LIB_FILENAME "${AVIF_SOURCE_DIR}/ext/libxml2/install.libavif/lib/${AVIF_LIBRARY_PREFIX}xml2${CMAKE_STATIC_LIBRARY_SUFFIX}")
 if(EXISTS "${LIB_FILENAME}")
diff --git a/ext/libxml2.cmd b/ext/libxml2.cmd
index ea39c7e..a9dc19a 100755
--- a/ext/libxml2.cmd
+++ b/ext/libxml2.cmd
@@ -5,7 +5,7 @@
 
 : # libxml2 is released under the MIT License.
 
-git clone -b v2.11.5 --depth 1 https://gitlab.gnome.org/GNOME/libxml2.git
+git clone -b v2.12.6 --depth 1 https://gitlab.gnome.org/GNOME/libxml2.git
 
 mkdir -p libxml2/build.libavif
 cmake libxml2 -B libxml2/build.libavif/ -G Ninja -DBUILD_SHARED_LIBS=OFF -DCMAKE_INSTALL_PREFIX=libxml2/install.libavif \
diff --git a/tests/docker/build.sh b/tests/docker/build.sh
index b2e7704..1c0c779 100644
--- a/tests/docker/build.sh
+++ b/tests/docker/build.sh
@@ -53,7 +53,7 @@
 
 # rav1e
 cd
-git clone -b v0.7.0 --depth 1 https://github.com/xiph/rav1e.git
+git clone -b v0.7.1 --depth 1 https://github.com/xiph/rav1e.git
 cd rav1e
 cargo cinstall --prefix=/usr --release