[gtk-osx] Set JHBUILD_RELEASE_VERSION and use it to ensure consistency for clone and reset.

[John Ralls <jralls src gnome org>]

commit 6d0d3649ad76da747a92ae9969b4f28249ec3987
Author: John Ralls <jralls ceridwen us>
Date:   Fri Aug 27 10:23:09 2021 -0700

    Set JHBUILD_RELEASE_VERSION and use it to ensure consistency for clone and reset.

 gtk-osx-setup.sh | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/gtk-osx-setup.sh b/gtk-osx-setup.sh
index 1d0087e9..5023b7c3 100755
--- a/gtk-osx-setup.sh
+++ b/gtk-osx-setup.sh
@@ -117,13 +117,14 @@ $PIP install --upgrade --user pipenv==2020.11.15
 pip_remove typing
 PIPENV="$PYTHONUSERBASE/bin/pipenv"
 
+JHUILD_RELEASE_VERSION=3.38.0
 # Install jhbuild
 if test ! -d "$DEV_SRC_ROOT/jhbuild/.git" ; then
-    git clone -b 3.36.0 $GITLAB/jhbuild.git "$DEV_SRC_ROOT/jhbuild"
+    git clone -b $JHBUILD_RELEASE_VERSION $GITLAB/jhbuild.git "$DEV_SRC_ROOT/jhbuild"
     cd "$DEV_SRC_ROOT/jhbuild"
 else #Get the latest if it's already installed
     cd "$DEV_SRC_ROOT/jhbuild"
-    git reset --hard 3.38.0
+    git reset --hard $JHBUILD_RELEASE_VERSION
 fi
 
 # Install Ninja