mkosi: Use tools tree by default

Let's enable usage of a tools tree by default to simplify the setup
for new contributors and save them from having to install or upgrade
a bunch of extra tools to get mkosi working as expected.

.github/workflows/coverage.yml

@@ -57,7 +57,6 @@ jobs:
           Distribution=arch
 
           [Build]
-          ToolsTree=default
           ToolsTreeDistribution=arch
           UseSubvolumes=yes
           WithTests=no

.github/workflows/mkosi.yml

@@ -152,7 +152,6 @@ jobs:
 
           [Build]
           UseSubvolumes=yes
-          ToolsTree=default
           ToolsTreeDistribution=fedora
           ToolsTreeRelease=rawhide
 

mkosi.conf

@@ -29,6 +29,7 @@ RepartDirectories=mkosi.repart
 OutputDirectory=build/mkosi.output
 
 [Build]
+ToolsTree=default
 BuildDirectory=build/mkosi.builddir
 CacheDirectory=build/mkosi.cache
 BuildSourcesEphemeral=yes