Fix regex test OOM (#47209)

Author: danmoseley

src/libraries/System.Text.RegularExpressions/tests/Regex.Match.Tests.cs

@@ -557,8 +557,9 @@ public void Match_DefaultTimeout_Throws(RegexOptions options)
         }
 
         // On 32-bit we can't test these high inputs as they cause OutOfMemoryExceptions.
+        // On Linux, we may get killed by the OOM Killer; on Windows, it will swap instead
         [OuterLoop("Can take several seconds")]
-        [ConditionalTheory(typeof(Environment), nameof(Environment.Is64BitProcess))]
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.Is64BitProcess), nameof(PlatformDetection.IsWindows))]
         [InlineData(@"a\s+", RegexOptions.None)]
         [InlineData(@"a\s+", RegexOptions.Compiled)]
         [InlineData(@"a\s+ ", RegexOptions.None)]
@@ -571,8 +572,9 @@ public void Match_Timeout_Loop_Throws(string pattern, RegexOptions options)
         }
 
         // On 32-bit we can't test these high inputs as they cause OutOfMemoryExceptions.
+        // On Linux, we may get killed by the OOM Killer; on Windows, it will swap instead
         [OuterLoop("Can take several seconds")]
-        [ConditionalTheory(typeof(Environment), nameof(Environment.Is64BitProcess))]
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.Is64BitProcess), nameof(PlatformDetection.IsWindows))]
         [InlineData(RegexOptions.None)]
         [InlineData(RegexOptions.Compiled)]
         public void Match_Timeout_Repetition_Throws(RegexOptions options)