Reduce running time of GitHub_19361 test case (dotnet/coreclr#23048)

This is a regression test and the original issue indicated that the test
would fail reliably under GC stress. So cut down the size of the lists
being processed and remove the various exclusions.

This reduces execution time on arm64 debug from ~30 mins to 2 seconds.

Closes dotnet/coreclr#20232.

Commit migrated from dotnet/coreclr@76abdef

src/coreclr/tests/issues.targets

@@ -535,9 +535,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/JIT/jit64/eh/FinallyExec/nonlocalexitinroot/*">
             <Issue>Test times out</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/GitHub_19361/GitHub_19361/*">
-            <Issue>20232</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/GC/Scenarios/DoublinkList/dlstack/*">
             <Issue>Release only crash</Issue>
         </ExcludeList>
@@ -569,9 +566,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/tracing/runtimeeventsource/runtimeeventsource/*">
             <Issue>19340</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/GitHub_19361/GitHub_19361/*">
-            <Issue>20232</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/GC/Scenarios/Dynamo/dynamo/*">
             <Issue>17129</Issue>
         </ExcludeList>

src/coreclr/tests/src/JIT/Regression/JitBlue/GitHub_19361/GitHub_19361.cs

@@ -46,7 +46,7 @@ public Test(Random rng, List<CompositeSource> sources)
         {
             var items = new List<(DateTime Date, CompositeSource Key, decimal Attribution)>();
 
-            foreach (var _ in Enumerable.Range(0, rng.Next(1000, 10000)))
+            foreach (var _ in Enumerable.Range(0, rng.Next(50, 100)))
             {
                 items.Add((
                     BaseDate.AddDays(rng.Next(1, 100)),
@@ -66,7 +66,7 @@ public static List<CompositeSource> GetCompositeSources()
         {
 
             var list = new List<CompositeSource>();
-            foreach (var _ in Enumerable.Range(0, 100))
+            foreach (var _ in Enumerable.Range(0, 50))
             {
                 lock (Rng)
                 {
@@ -89,7 +89,7 @@ static int Main()
         {
             Console.WriteLine("Starting stress loop");
             var compositeSources = GetCompositeSources();
-            var res = Parallel.For(0, 10, i =>
+            var res = Parallel.For(0, 5, i =>
             {
                 int seed;
                 lock (Rng)