python3: Simplify ptest exclusion list

Makes the exclusion list a bit more readable, avoiding very long sed
expression lines.

[Kris Gavvala]:
this commit was modified to fit scarthgap. the original commit expects
to skip test_timerfd_TFD_TIMER_ABSTIME, test_date_locale2 and test_null_dlsym.
These tests were not being skipped on scarthgap so were removed from the
backport.

(From OE-Core rev: 649b6848ccd4aa3842b2b42b03058511e4f07ce3)

Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Kris Gavvala <kris.gavvala@windriver.com>
(cherry picked from commit d9a44e7390d7c8f2c2b73572825a6f8ceeb729ac)
Signed-off-by: Yoann Congal <yoann.congal@smile.fr>
Signed-off-by: Paul Barker <paul@pbarker.dev>

meta/recipes-devtools/python/python3_3.12.13.bb

@@ -256,8 +256,19 @@ do_install:append:class-nativesdk () {
     create_wrapper ${D}${bindir}/python${PYTHON_MAJMIN} TERMINFO_DIRS='${sysconfdir}/terminfo:/etc/terminfo:/usr/share/terminfo:/usr/share/misc/terminfo:/lib/terminfo' PYTHONNOUSERSITE='1'
 }
 
-do_install_ptest:append:class-target:libc-musl () {
-    sed -i -e 's|SKIPPED_TESTS=|SKIPPED_TESTS="-x test__locale -x test_c_locale_coercion -x test_locale -x test_os test_re -x test__xxsubinterpreters -x test_threading"|' ${D}${PTEST_PATH}/run-ptest
+
+SKIPPED_TESTS:append:class-target:libc-musl = " \
+    -x test__locale \
+    -x test_c_locale_coercion \
+    -x test_locale \
+    -x test_os test_re \
+    -x test__xxsubinterpreters \
+    -x test_threading \
+"
+
+
+do_install_ptest:append () {
+    sed -i -e "s|SKIPPED_TESTS=|SKIPPED_TESTS=\"${SKIPPED_TESTS}\"|" ${D}${PTEST_PATH}/run-ptest
 }
 
 SYSROOT_PREPROCESS_FUNCS:append:class-target = " provide_target_config_script"