meta-python: Convert confusing appends to override syntax

While in this case `RDEPENDS:class-target +=` wouldn't result in any
unwanted override, there is no guarantee there won't be a change, which
would be hidden by this override. To avoid any surprises in the future
let's use `:append:class-target =` syntax here.

Signed-off-by: Michal Sieron <michalwsieron@gmail.com>
Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>

meta-python/recipes-devtools/python/python3-yamlloader_1.6.0.bb

@@ -11,6 +11,6 @@ DEPENDS += "\
     python3-hatch-vcs-native \
 "
 
-RDEPENDS:${PN}:class-target += "\
+RDEPENDS:${PN}:append:class-target = " \
     python3-pyyaml \
 "