auth/nkeys-jwts/go no longer works

### Observed behavior

```shell
> nbe run auth/nkeys-jwts/go
[+] Building 26.8s (12/13) docker:desktop-linux
=> [internal] load build definition from Dockerfile 0.1s
=> => transferring dockerfile: 291B 0.0s
=> [internal] load metadata for docker.io/library/golang:1.21.4-alpine3.18 1.8s
=> [internal] load metadata for docker.io/library/alpine:latest 1.8s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [build 1/6] FROM docker.io/library/golang:1.21.4-alpine3.18@sha256:70afe55365a265f0762257550bc38440e0d6d6b97020d3f8c85328f00200dd8e 18.3s
=> => resolve docker.io/library/golang:1.21.4-alpine3.18@sha256:70afe55365a265f0762257550bc38440e0d6d6b97020d3f8c85328f00200dd8e 0.0s
=> => sha256:4e09ca4c01cabba257942296eac2fdbe5c750c8e03b63a834d5c126f67ae488f 1.16kB / 1.16kB 0.0s
=> => sha256:72d77ba3e25b71d7b1b4da78bec9e02d992e29f51e495bc21e76afe205ee054d 6.32kB / 6.32kB 0.0s
=> => sha256:c926b61bad3b94ae7351bafd0c184c159ebf0643b085f7ef1d47ecdc7316833c 3.40MB / 3.40MB 0.7s
=> => sha256:5501dced60f86be38cc73d3c038f7db4afeee65726f7e422aacf09244539ebf1 284.70kB / 284.70kB 0.2s
=> => sha256:1db2698d032ff0a64cc284ce403f9c4a3bc79a5d51138807a5ffc79f2e0c7aa9 67.00MB / 67.00MB 2.7s
=> => sha256:70afe55365a265f0762257550bc38440e0d6d6b97020d3f8c85328f00200dd8e 1.65kB / 1.65kB 0.0s
=> => sha256:e3198207dabfb827404f6d6e220ab586270b4c030d81b23ea8dfcb3d45e7c415 156B / 156B 0.5s
=> => extracting sha256:c926b61bad3b94ae7351bafd0c184c159ebf0643b085f7ef1d47ecdc7316833c 0.5s
=> => extracting sha256:5501dced60f86be38cc73d3c038f7db4afeee65726f7e422aacf09244539ebf1 0.1s
=> => extracting sha256:1db2698d032ff0a64cc284ce403f9c4a3bc79a5d51138807a5ffc79f2e0c7aa9 14.8s
=> => extracting sha256:e3198207dabfb827404f6d6e220ab586270b4c030d81b23ea8dfcb3d45e7c415 0.0s
=> [internal] load build context 0.0s
=> => transferring context: 15.04kB 0.0s
=> [stage-1 1/2] FROM docker.io/library/alpine:latest@sha256:a8560b36e8b8210634f77d9f7f9efd7ffa463e380b75e2e74aff4511df3ef88c 1.7s
=> => resolve docker.io/library/alpine:latest@sha256:a8560b36e8b8210634f77d9f7f9efd7ffa463e380b75e2e74aff4511df3ef88c 0.0s
=> => sha256:1c4eef651f65e2f7daee7ee785882ac164b02b78fb74503052a26dc061c90474 1.02kB / 1.02kB 0.0s
=> => sha256:aded1e1a5b3705116fa0a92ba074a5e0b0031647d9c315983ccba2ee5428ec8b 581B / 581B 0.0s
=> => sha256:a8560b36e8b8210634f77d9f7f9efd7ffa463e380b75e2e74aff4511df3ef88c 9.22kB / 9.22kB 0.0s
=> => sha256:f18232174bc91741fdf3da96d85011092101a032a93a388b79e99e69c2d5c870 3.64MB / 3.64MB 0.9s
=> => extracting sha256:f18232174bc91741fdf3da96d85011092101a032a93a388b79e99e69c2d5c870 0.6s
=> [build 2/6] WORKDIR /opt/app 0.6s
=> [build 3/6] COPY go.mod go.sum ./ 0.0s
=> [build 4/6] RUN go mod download && go mod verify 5.3s
=> [build 5/6] COPY . ./ 0.0s
=> ERROR [build 6/6] RUN go build -v -o /app ./... 0.5s
------
> [build 6/6] RUN go build -v -o /app ./...:
0.412 main.go:7:2: no required module provides package github.com/nats-io/jwt/v2; to add it:
0.412 go get github.com/nats-io/jwt/v2
------
Dockerfile:9
--------------------
7 |
8 | COPY . ./
9 | >>> RUN go build -v -o /app ./...
10 |
11 | FROM alpine
--------------------
ERROR: failed to solve: process "/bin/sh -c go build -v -o /app ./..." did not complete successfully: exit code: 1
build image: exit status 1
```

### Expected behavior

As shown https://natsbyexample.com/examples/auth/nkeys-jwts/go

### Server and client version

> docker --version
Docker version 28.0.1, build 068a01ea94
@ [darwin-amd64.zip]
and
docker --version ─╯
Docker version 28.0.0, build f9ced58158
@ [darwin-arm64.zip]

### Host environment

Tested on two MacOS 15.3.2 (24D81) (Intel and M4)

### Steps to reproduce

> nbe run auth/nkeys-jwts/go

Start with auth/nkeys-jwts/go/main.go and the example's Dockerfile, then run nbe run auth/nkeys-jwts/go to reproduce the missing-module build error. Check the example's go.mod and go.sum during the build; done means the image builds successfully and the example matches the behavior shown on natsbyexample.com.

Written by the indexing model from the issue text.