testsuite: Compile T9630 with +RTS -G1

For the reasons described in Note [residency] we run programs with -G1
when we care about the max_bytes_used metric.

testsuite/tests/perf/compiler/all.T

@@ -382,7 +382,10 @@ test('Naperian',
 
 test ('T9630',
       [ collect_compiler_stats('max_bytes_used',15), # Note [residency]
-      extra_clean(['T9630a.hi', 'T9630a.o'])
+      extra_clean(['T9630a.hi', 'T9630a.o']),
+
+      # Use `+RTS -G1` for more stable residency measurements. Note [residency].
+      extra_hc_opts('+RTS -G1 -RTS')
       ],
       multimod_compile,
       ['T9630', '-v0 -O'])