HdyArrows: Use alredy computed values

This improves readability a bit
7 jobs for arrows in 11 minutes and 46 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Build
passed #227721
librem5
build-debian-clang

00:03:58

passed #227719
librem5
build-debian-gcc

00:02:48

passed #227720
librem5
build-debian-gcc-static

00:02:44

passed #227722
librem5
build-fedora-gcc

00:02:48

 
  Docs
passed #227723
librem5
build-gtkdoc

00:01:59

 
  Test
passed #227724
librem5
unit-test

00:01:40

44.9%
 
  Package
passed #227725
librem5
package-debian

00:02:28