ci: shorter random fuzzing in clang-msan-fuzz-unoptimized

The fuzzer unit tests take 4 to 12 min at -O0 under MSan, depending on
the runner, and are what this job is for. The random fuzzing that
follows (fuzzer 200 s, zstreamtest 2x 90 s) duplicates clang-msan-fuzz,
which runs it longer, with --long-tests, on optimized code.

Cut it to 60 s and 2x 30 s: ~2.3 min less on this job, the longest of
dev-long-tests after the previous changes.

.github/workflows/dev-long-tests.yml

diff --git a/.github/workflows/dev-long-tests.yml b/.github/workflows/dev-long-tests.yml
index 753085f..fab0b96 100644
--- a/.github/workflows/dev-long-tests.yml
+++ b/.github/workflows/dev-long-tests.yml
@@ -231,10 +231,12 @@
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # tag=v7.0.1
       - name: clang + MSan + Fuzz Test
+        # -O0 targets the unit tests on unoptimized code: random fuzzing is kept short.
+        # clang-msan-fuzz runs the long random fuzzing.
         run: |
           sudo apt-get -qqq update
           sudo apt-get install clang
-          CC=clang MOREFLAGS="-O0" make clean msan-fuzztest
+          CC=clang MOREFLAGS="-O0" FUZZERTEST=-T60s ZSTREAM_TESTTIME=-T30s make clean msan-fuzztest
 
   clang-msan-fuzz:
     runs-on: ubuntu-latest