woodpecker exec intermittently switches between local and docker backends

[alexmt]

Component

cli

Describe the bug

The woodpecker exec command is not consistent when run on the machine with docker installed. . It intermittently switches between local and docker backends.

Steps to reproduce:

To reproduce try to execute the following pipeline multiple times:

.woodpecker.yaml

pipeline:
  step1:
    image: golang
    commands:
      - echo step1

while true; do  woodpecker exec .woodpecker.yaml; done
[step1:L0:0s] + echo step1
[step1:L1:0s] step1
[step1:L0:0s] + echo step1
[step1:L1:0s] step1
[step1:L0:0s] + echo step1
[step1:L1:0s] step1
[step1:L0:0s] + echo step1
[step1:L1:0s] step1
[step1:L0:0s] Backend engine error while running step: exec: "golang": executable file not found in $PATH1:48PM FTL error running cli error="exec: \"golang\": executable file not found in $PATH"
[step1:L0:0s] + echo step1
[step1:L1:0s] step1
[step1:L0:0s] Backend engine error while running step: exec: "golang": executable file not found in $PATH1:48PM FTL error running cli error="exec: \"golang\": executable file not found in $PATH"
[step1:L0:0s] Backend engine error while running step: exec: "golang": executable file not found in $PATH1:48PM FTL error running cli error="exec: \"golang\": executable file not found in $PATH"

Periodically woodpecker chooses to use the local backend.

Expected Behavior:

CLI should consistently choose the same backend. IMHO docker backend should take priority over local backend.

System Info

woodpecker-cli --version                                                                                    
woodpecker-cli version 0.15.6

### Additional context

_No response_

### Validations

- [X] Read the [Contributing Guidelines](https://github.com/woodpecker-ci/woodpecker/blob/master/CONTRIBUTING.md).
- [X] Read the [docs](https://woodpecker-ci.org/docs/intro).
- [X] Check that there isn't [already an issue](https://github.com/woodpecker-ci/woodpecker/issues) that reports the same bug to avoid creating a duplicate.
- [X] Checked that the bug isn't fixed in the `next` version already [https://woodpecker-ci.org/faq#which-version-of-woodpecker-should-i-use]
- [X] Check that this is a concrete bug. For Q&A join our [Discord Chat Server](https://discord.gg/fcMQqSMXJy) or the [Matrix room](https://matrix.to/#/#woodpecker:matrix.org).