Update buildkite agent and set instance type

.buildkite/sanitizers.yml

@@ -21,7 +21,8 @@ steps:
         echo "--- :beers: Done"
     label: ":_: Undefined Sanitizer"
     agents:
-      - "role=automation-builder-large"
+      role: 'automation-builder-fleet'
+      aws:instance-type: 'm5d.2xlarge'
     artifact_paths:
       - "build.tar.gz"
       - "ninja.log"
@@ -64,7 +65,8 @@ steps:
         echo "--- :beers: Done"
     label: ":_: Address Sanitizer"
     agents:
-      - "role=automation-builder-large"
+      role: 'automation-builder-fleet'
+      aws:instance-type: 'm5d.2xlarge'
     artifact_paths:
       - "build.tar.gz"
       - "ninja.log"
@@ -96,7 +98,8 @@ steps:
         ctest -j8 -LE _tests -V -O sanitizer.log || true
     label: ":_: Undefined Sanitizer Tests"
     agents:
-      - "role=automation-builder-large"
+      role: 'automation-builder-fleet'
+      aws:instance-type: 'm5d.2xlarge'
     artifact_paths:
       - "mongod.log"
       - "sanitizer.log"
@@ -118,7 +121,8 @@ steps:
         ctest -j8 -LE _tests -V -O sanitizer.log || true
     label: ":_: Address Sanitizer Tests"
     agents:
-      - "role=automation-builder-large"
+      role: 'automation-builder-fleet'
+      aws:instance-type: 'm5d.2xlarge'
     artifact_paths:
       - "mongod.log"
       - "sanitizer.log"