Rename test_memcheck to test_valgrind

Valgrind is what it does. `memcheck` is how it's implemented.
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 55f554b..039b1b8 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -1158,7 +1158,7 @@
     fi
 }
 
-component_test_memcheck () {
+component_test_valgrind () {
     msg "build: Release (clang)"
     CC=clang cmake -D CMAKE_BUILD_TYPE:String=Release .
     make