fix(runners): wire job_retry.lambda_memory_size and lambda_timeout (github-aws-runners#5120)

## Description
Both `var.job_retry` (in `modules/multi-runner/variables.tf` and
`modules/runners/variables.tf`) declare `lambda_memory_size` and
`lambda_timeout` as documented configuration fields, but
`local.job_retry` in
[`modules/runners/job-retry.tf`](https://github.com/github-aws-runners/terraform-aws-github-runner/blob/main/modules/runners/job-retry.tf#L5-L33)
never copies either field into the `config` map passed to the inner
`job-retry` / `lambda` sub-modules. The inner lambda module then falls
back to its defaults (`memory_size = 256`, `timeout = 60`), so
user-supplied values are silently dropped — `tofu plan` shows no diff
and the running Lambda keeps its defaults.

The fix is a two-line addition to the `local.job_retry` map. It mirrors
the pattern `modules/runners/ssm-housekeeper.tf` already uses for
`local.ssm_housekeeper.lambda_memory_size` /
`local.ssm_housekeeper.lambda_timeout` — that Lambda correctly threads
the values through.

## Motivation
Discovered in production: I pinned `lambda_memory_size = 512` in
`multi_runner_config[*].runner_config.job_retry` after observing the
job-retry Lambdas at 87% memory utilisation (223 MB peak on the 256 MB
default), and got `No changes` from `tofu plan`. Tracing the wiring
confirmed the value never reaches the resource.

## Reproduction
```hcl
module "runners" {
  source  = "github-aws-runners/github-runner/aws//modules/multi-runner"
  version = "7.6.0"
  # …
  multi_runner_config = {
    "example" = {
      matcherConfig = { … }
      runner_config = merge(local.default_config, {
        # … other config …
        job_retry = {
          enable             = true
          lambda_memory_size = 512  # ← silently ignored before this PR
          lambda_timeout     = 60   # ← silently ignored before this PR
        }
      })
    }
  }
}
```
After this fix, `tofu plan` shows the expected `memory_size: 256 -> 512`
change on the job-retry Lambda.

## Verification
- `tofu fmt` clean.
- The variable type definition on both `modules/runners/variables.tf`
and `modules/multi-runner/variables.tf` already declares
`lambda_memory_size = optional(number, 256)` and `lambda_timeout =
optional(number, 30)`, so no public surface changes.
- The inner `modules/runners/modules/lambda` accepts `memory_size` and
`timeout` on its `lambda` input object (with the same defaults), so when
the wiring is restored the values flow through naturally.

## No-impact when not set
Defaults remain `memory_size = 256` (per the variable declaration) and
`timeout = 30` — same as today's effective values when nothing is
overridden.

Co-authored-by: Brend Smits <brend.smits@philips.com>

Author: oscarbc96

modules/runners/job-retry.tf

@@ -30,6 +30,8 @@ locals {
     ghes_url                                                       = var.ghes_url
     lambda_event_source_mapping_batch_size                         = var.lambda_event_source_mapping_batch_size
     lambda_event_source_mapping_maximum_batching_window_in_seconds = var.lambda_event_source_mapping_maximum_batching_window_in_seconds
+    memory_size                                                    = var.job_retry.lambda_memory_size
+    timeout                                                        = var.job_retry.lambda_timeout
   }
 }