pre-commit: run tests instead of just build

.githooks/pre-commit

···
 #!/bin/sh
-# check formatting and build before commit
+# check formatting, build, and test before commit
 
 zig fmt --check src/ build.zig 2>/dev/null
 if [ $? -ne 0 ]; then
···
     exit 1
 fi
 
-zig build 2>/dev/null
+zig build test 2>/dev/null
 if [ $? -ne 0 ]; then
-    echo "zig build failed."
+    echo "zig build test failed."
     exit 1
 fi