Add GC-safe region around Highs_run

Prevent a long-running `Highs_run` call from blocking GC (and
freezing the other Julia threads).

src/gen/libhighs.jl

@@ -282,7 +282,19 @@ Optimize a model. The algorithm used by HiGHS depends on the options that have b
 A `kHighsStatus` constant indicating whether the call succeeded.
 """
 function Highs_run(highs)
-    ccall((:Highs_run, libhighs), HighsInt, (Ptr{Cvoid},), highs)
+    r = 0
+    # if `Highs_run` implicitly uses memory or other resources owned by `highs`, preserve it
+    GC.@preserve highs begin
+        # allow Julia to GC while this thread is in `Highs_run`
+        gc_state = ccall(:jl_gc_safe_enter, Int8, ())
+
+        r = ccall((:Highs_run, libhighs), HighsInt, (Ptr{Cvoid},), highs)
+
+        # leave GC-safe region, waiting for GC to complete if it's running
+        ccall(:jl_gc_safe_leave, Cvoid, (Int8,), gc_state)
+    end
+
+    return r
 end
 
 """