Increase max runners available for m4.10xlarge (#5514)

We can estimate the maximum number of m4.10xlarge runners based on the
max runner number for linux.16xlarge.spr.

Per our statistic, in one round of CI inductor test, dynamo suites
freezing accuracy test and inductor UT test run on m4.10xlarge, they
cost ~9h. dynamo suites freezing accuracy test also runs on
linux.16xlarge.spr, it cost ~3h.

Based on the time cost ratio (9/3) and the max runner number for
linux.16xlarge.spr (150), 450 should be enough for the maximum number of
m4.10xlarge.

.github/scale-config.yml

@@ -31,7 +31,7 @@ runner_types:
     disk_size: 200
     instance_type: m4.10xlarge
     is_ephemeral: false
-    max_available: 60
+    max_available: 450
     os: linux
   linux.24xl.spr-metal:
     disk_size: 200