Provenance flag is not handled correctly for boolean passed

### Description

sudo nerdctl build . --provenance=false -t test:0.1

creates a unkown/unkown image tag

```
[shubhum@lima-finch Test]$ sudo nerdctl image ls
REPOSITORY TAG IMAGE ID CREATED PLATFORM SIZE BLOB SIZE
test 0.1 3e7b5c47d20a 7 seconds ago linux/amd64 8.978MB 3.798MB
test 0.1 3e7b5c47d20a 7 seconds ago unknown/unknown 0B 3.099kB
```

### Steps to reproduce the issue

1. sudo nerdctl build . --provenance=false -t test:0.1

2.
```
[shubhum@lima-finch Test]$ sudo nerdctl image ls
REPOSITORY TAG IMAGE ID CREATED PLATFORM SIZE BLOB SIZE
test 0.1 3e7b5c47d20a 7 seconds ago linux/amd64 8.978MB 3.798MB
test 0.1 3e7b5c47d20a 7 seconds ago unknown/unknown 0B 3.099kB
```

### Describe the results you received and expected

It should not create image with platform unknown/unknown

### What version of nerdctl are you using?

nerdctl 2.1.2

### Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

### Host information

_No response_