test: cover c2a/s2a CPU SKUs in supportsFS table

Pin the c2a/s2a entries that are in the supportedTypes map; the table
previously only asserted c1a/s1a. Review nit.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: npujari-crusoe

internal/node/fs/util_test.go

@@ -17,6 +17,8 @@ func TestSupportsFS(t *testing.T) {
 		// CPU instances always support shared FS, regardless of slice count.
 		{name: "c1a", instanceType: "c1a.16x", want: true},
 		{name: "s1a", instanceType: "s1a.8x", want: true},
+		{name: "c2a", instanceType: "c2a.4x", want: true},
+		{name: "s2a", instanceType: "s2a.2x", want: true},
 
 		// L40s: supported on any slice count (CRUSOE-67560). The full-node
 		// .10x case must keep working; smaller slices must now also pass.