Bump rshell dependency from v0.0.13 to v0.0.14 (#49958)

### What does this PR do?

- Bumps `github.com/DataDog/rshell` from `v0.0.13` to `v0.0.14`. No call-site changes.

### Motivation

- v0.0.13..v0.0.14 contains a single commit, [DataDog/rshell#200](DataDog/rshell#200), which adds an opt-in `interp.WarningsWriter(io.Writer)` option and a `Runner.Warnings() []string` accessor. Today's PAR rshell handler does not pass either, so behaviour is byte-for-byte unchanged: sandbox warnings continue to fall back to `r.stderr`, which is where the handler already routes them.
- This bump lands in isolation so the follow-up PR — wiring the new accessor into `RunCommandOutputs.SandboxWarnings` to fix [DataDog/rshell#191](DataDog/rshell#191) — is a clean, reviewable diff with no `go.mod`/`go.sum` noise.

### Describe how you validated your changes

- `go get github.com/DataDog/rshell@v0.0.14` — single-line `go.mod` change, expected `go.sum` update.
- `go build ./pkg/privateactionrunner/...` — clean.
- `go test -count=1 ./pkg/privateactionrunner/bundles/remoteaction/rshell/...` — all tests pass.

### Additional Notes

- Follow-up PR (forthcoming) will wire `runner.Warnings()` into the PAR rshell handler's response. The corresponding contract change in dd-source (additive `sandboxWarnings?: string[]` field on `RunCommandOutputs`) is open at [DataDog/dd-source#423305](DataDog/dd-source#423305).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: matthew.deguzman <matthew.deguzman@datadoghq.com>

Author: matt-dz

go.mod

@@ -966,7 +966,7 @@ require (
 	github.com/DataDog/datadog-agent/pkg/util/cgroups v0.64.0-rc.3
 	github.com/DataDog/datadog-agent/pkg/util/kubernetes/apiserver/common/namespace v0.77.0-devel.0.20260211235139-a5361978c2b6
 	github.com/DataDog/ddtrivy v0.0.0-20260115083325-07614fb0b8d5
-	github.com/DataDog/rshell v0.0.13
+	github.com/DataDog/rshell v0.0.14
 	github.com/aws/aws-sdk-go-v2/service/secretsmanager v1.41.0
 	github.com/aws/aws-sdk-go-v2/service/ssm v1.67.8
 	github.com/aymerick/raymond v2.0.2+incompatible

go.sum

@@ -0,0 +1,4 @@
+---
+enhancements:
+  - |
+    Bump ``rshell`` to v0.0.14.