dev-libs/protobuf: fix tests

'full-test' requires this. TestSourceDir in src/google/protobuf/testing/googletest.cc
respects 'srcdir' as an env var as a hint.

Bug: https://bugs.gentoo.org/934062
Signed-off-by: Sam James <sam@gentoo.org>

dev-libs/protobuf/protobuf-22.5-r1.ebuild

@@ -83,6 +83,11 @@ src_compile() {
 	fi
 }
 
+src_test() {
+	local -x srcdir="${S}"/src
+	cmake-multilib_src_test
+}
+
 multilib_src_install_all() {
 	find "${ED}" -name "*.la" -delete || die
 

dev-libs/protobuf/protobuf-23.3-r3.ebuild

@@ -74,6 +74,11 @@ src_compile() {
 	fi
 }
 
+src_test() {
+	local -x srcdir="${S}"/src
+	cmake-multilib_src_test
+}
+
 multilib_src_install_all() {
 	find "${ED}" -name "*.la" -delete || die
 

dev-libs/protobuf/protobuf-26.1-r1.ebuild

@@ -72,6 +72,11 @@ src_compile() {
 	fi
 }
 
+src_test() {
+	local -x srcdir="${S}"/src
+	cmake-multilib_src_test
+}
+
 multilib_src_install_all() {
 	find "${ED}" -name "*.la" -delete || die