bench: Add Graviton5 (c9g) to EC2 benchmark matrix

Adds a c9g.medium row to the ec2_all matrix in bench.yml so benchmarks
also run on Neoverse V3 / Graviton5, alongside the existing Graviton2/3/4
entries. Configuration mirrors Graviton4 (aarch64 AMI, armv9-a+sha3,
-flto, PERF).

- Resolves #1774

Signed-off-by: Matthias J. Kannwischer <matthias@zerorisc.com>

Author: mkannwischer

.github/workflows/bench.yml

@@ -127,6 +127,13 @@ jobs:
             cflags: "-flto -DMLK_FORCE_AARCH64"
             ldflags: "-flto"
             perf: PERF
+          - name: Graviton5
+            ec2_instance_type: c9g.medium
+            ec2_ami: ubuntu-latest (aarch64)
+            archflags: -march=armv9-a+sha3
+            cflags: "-flto -DMLK_FORCE_AARCH64"
+            ldflags: "-flto"
+            perf: PERF
           - name: AMD EPYC 4th gen (c7a)
             ec2_instance_type: c7a.medium
             ec2_ami: ubuntu-latest (x86_64)