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-zopeinterface_8.2.bb

@@ -11,7 +11,7 @@ PACKAGES =. "${PN}-test "
 
 RPROVIDES:${PN} += "zope-interfaces"
 
-RDEPENDS:${PN}:class-target += "python3-datetime"
+RDEPENDS:${PN}:append:class-target = " python3-datetime"
 RDEPENDS:${PN}-test += "python3-unittest python3-doctest"
 
 FILES:${PN}-dbg += "${PYTHON_SITEPACKAGES_DIR}/*.egg/*/*/.debug"