CI: drone: skip some ReleaseFast and ReleaseSmall std lib tests

Follow-up commit to b9103bd514.

ci/drone/test_linux_std_ReleaseFast

@@ -13,4 +13,5 @@ $ZIG build test-std \
   -Dskip-release-safe \
   -Dskip-release-small \
   -Dskip-non-native \
-  -Dskip-single-threaded
+  -Dskip-single-threaded \
+  -Dskip-libc

ci/drone/test_linux_std_ReleaseSmall

@@ -7,10 +7,11 @@ INSTALL_PREFIX="$DRONE_WORKSPACE/stage3-release"
 ZIG="$INSTALL_PREFIX/bin/zig"
 export ZIG_GLOBAL_CACHE_DIR="$DRONE_WORKSPACE/zig-cache"
 
-# Empirically, this takes about 55 minutes on the CI, and is the bottleneck
-# causing timeouts. So this is disabled in favor of running a smaller set
-# of ReleaseSmall std lib tests.
-# $ZIG build test-std -Dskip-debug -Dskip-release-safe -Dskip-release-fast -Dskip-non-native
-
-$ZIG test lib/std/std.zig -OReleaseSmall     --zig-lib-dir lib
-$ZIG test lib/std/std.zig -OReleaseSmall -lc --zig-lib-dir lib
+$ZIG build test-std \
+  --zig-lib-dir lib \
+  -Dskip-debug \
+  -Dskip-release-safe \
+  -Dskip-release-fast \
+  -Dskip-non-native \
+  -Dskip-single-threaded \
+  -Dskip-libc