iceberg: wire the module into CI

- ci/ci.sh: new ICEBERG environment variable, printed in the
  reproduction header and passed to configure as
  --enable-module-iceberg (mirroring CHILLDKG); bench_iceberg runs in
  the bench step when the module is enabled, as in the source tree's
  CI.
- .github/workflows/ci.yml: ICEBERG: 'no' default; ICEBERG: 'yes' in
  the 20 jobs that enable musig + schnorrsig + experimental (the same
  jobs that build chilldkg). Jobs that deliberately build without
  musig or its dependencies are left at 'no'. Verified
  programmatically: the YAML parses and every ICEBERG: 'yes' context
  also has MUSIG, SCHNORRSIG and EXPERIMENTAL set to 'yes'.

ci/ci.sh

@@ -15,7 +15,7 @@ print_environment() {
             ECMULTWINDOW ECMULTGENKB ASM WIDEMUL WITH_VALGRIND EXTRAFLAGS \
             EXPERIMENTAL ECDH RECOVERY EXTRAKEYS SCHNORRSIG MUSIG SCHNORRSIG_HALFAGG ELLSWIFT \
             ECDSA_S2C GENERATOR RANGEPROOF SURJECTIONPROOF WHITELIST ECDSAADAPTOR BPPP \
-            FROST CHILLDKG SECP256K1_TEST_ITERS BENCH SECP256K1_BENCH_ITERS CTIMETESTS SYMBOL_CHECK \
+            FROST CHILLDKG ICEBERG SECP256K1_TEST_ITERS BENCH SECP256K1_BENCH_ITERS CTIMETESTS SYMBOL_CHECK \
             EXAMPLES \
             HOST WRAPPER_CMD \
             CC CFLAGS CPPFLAGS AR NM \
@@ -71,6 +71,7 @@ fi
     --enable-module-schnorrsig-halfagg="$SCHNORRSIG_HALFAGG" \
     --enable-module-frost="$FROST" \
     --enable-module-chilldkg="$CHILLDKG" \
+    --enable-module-iceberg="$ICEBERG" \
     --enable-examples="$EXAMPLES" \
     --enable-ctime-tests="$CTIMETESTS" \
     --with-valgrind="$WITH_VALGRIND" \
@@ -134,6 +135,10 @@ then
         then
             $EXEC ./bench_bppp
         fi
+        if [ "$ICEBERG" = "yes" ]
+        then
+            $EXEC ./bench_iceberg
+        fi
     } >> bench.log 2>&1
 fi