Update GwpAsanUnified field trial parameters

I accidentally used the wrong parameters in this field trial testing
config (it should sample processes half as often.)

Bug: 973167
Change-Id: I0a26dd365e3a3cb5bbcc860ba9693295e1f912bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1744688
Auto-Submit: Vlad Tsyrklevich <vtsyrklevich@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#685543}

testing/variations/fieldtrial_testing_config.json

@@ -2449,7 +2449,7 @@
                         "MaxAllocations": "70",
                         "MaxMetadata": "255",
                         "ProcessSamplingBoost2": "10",
-                        "ProcessSamplingProbability": "0.1"
+                        "ProcessSamplingProbability": "0.05"
                     },
                     "enable_features": [
                         "GwpAsanMalloc",