Fix bash ternary in `//benchmarks:size_data` (#18234)

Replaces pseudocode bash ternary with working bash ternary.

Closes #18234

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/18234 from tempoz:tempoz-fix-bash-ternary b43be78388
PiperOrigin-RevId: 676861548

benchmarks/BUILD

@@ -235,7 +235,7 @@ genrule(
     ),
     outs = ["size_data.txt"],
     # We want --format=GNU which counts rodata with data, not text.
-    cmd = "size $$($$OSTYPE == 'linux-gnu' ? '--format=GNU -d' : '') $(SRCS) > $@",
+    cmd = "size $$([ $$OSTYPE == 'linux-gnu' ] && echo '--format=GNU -d' || echo '') $(SRCS) > $@",
     # "size" sometimes isn't available remotely.
     local = 1,
     tags = ["no-remote-exec"],