special_env_vars: add ESYSROOT and SYSROOT to environ_whitelist

Since these variables are filtered from the peristent ebuild environment
by the __filter_readonly_variables function, they have to be whitelisted
so that the config.environ() method allow them to pass through.

Fixes: a41dacf7926c ("Export SYSROOT and ESYSROOT in ebuild env in EAPI 7")
Reported-by: James Le Cuirot <chewi@gentoo.org>
diff --git a/pym/portage/package/ebuild/_config/special_env_vars.py b/pym/portage/package/ebuild/_config/special_env_vars.py
index 3323ff0..a308518 100644
--- a/pym/portage/package/ebuild/_config/special_env_vars.py
+++ b/pym/portage/package/ebuild/_config/special_env_vars.py
@@ -46,7 +46,7 @@
 	"DISTDIR", "DOC_SYMLINKS_DIR", "EAPI", "EBUILD",
 	"EBUILD_FORCE_TEST",
 	"EBUILD_PHASE", "EBUILD_PHASE_FUNC", "ECLASSDIR", "ECLASS_DEPTH", "ED",
-	"EMERGE_FROM", "EPREFIX", "EROOT",
+	"EMERGE_FROM", "EPREFIX", "EROOT", "ESYSROOT",
 	"FEATURES", "FILESDIR", "HOME", "MERGE_TYPE", "NOCOLOR", "PATH",
 	"PKGDIR",
 	"PKGUSE", "PKG_LOGDIR", "PKG_TMPDIR",
@@ -77,7 +77,7 @@
 	"PORTAGE_VERBOSE", "PORTAGE_WORKDIR_MODE", "PORTAGE_XATTR_EXCLUDE",
 	"PORTDIR", "PORTDIR_OVERLAY", "PREROOTPATH", "PYTHONDONTWRITEBYTECODE",
 	"REPLACING_VERSIONS", "REPLACED_BY_VERSION",
-	"ROOT", "ROOTPATH", "T", "TMP", "TMPDIR",
+	"ROOT", "ROOTPATH", "SYSROOT", "T", "TMP", "TMPDIR",
 	"USE_EXPAND", "USE_ORDER", "WORKDIR",
 	"XARGS", "__PORTAGE_TEST_HARDLINK_LOCKS",
 ]