ci: fix container image name when multiple given

[mrpollo]

When this workflow triggered by a tag push event, then it tags the image in multiple ways eg:

"image.name": "ghcr.io/px4/px4-dev:v1.16.0-alpha1,ghcr.io/px4/px4-dev:latest"

Having multiple names messes up the execution of the next step in the chain since we depend on its name to complete the testing.

Error https://github.com/PX4/PX4-Autopilot/actions/runs/11943677314/job/33293165630#step:10:3

[dagar]

Still unhappy.

[github-actions[bot]]

FLASH Analysis

px4_fmu-v5x

``` FILE SIZE VM SIZE -------------- -------------- +0.0% +24 +0.0% +24 .text -0.1% -24 [ = ] 0 [Unmapped] [ = ] 0 +0.0% +24 TOTAL ```

px4_fmu-v6x

``` FILE SIZE VM SIZE -------------- -------------- +0.0% +24 +0.0% +24 .text -0.0% -24 [ = ] 0 [Unmapped] [ = ] 0 +0.0% +24 TOTAL ```

[github-actions[bot]]

FLASH Analysis

px4_fmu-v5x

``` FILE SIZE VM SIZE -------------- -------------- +0.0% +24 +0.0% +24 .text -0.1% -24 [ = ] 0 [Unmapped] [ = ] 0 +0.0% +24 TOTAL ```

px4_fmu-v6x

``` FILE SIZE VM SIZE -------------- -------------- +0.0% +24 +0.0% +24 .text -0.0% -24 [ = ] 0 [Unmapped] [ = ] 0 +0.0% +24 TOTAL ```

[github-actions[bot]]

FLASH Analysis

px4_fmu-v5x

``` FILE SIZE VM SIZE -------------- -------------- +0.0% +24 +0.0% +24 .text -0.1% -24 [ = ] 0 [Unmapped] [ = ] 0 +0.0% +24 TOTAL ```

px4_fmu-v6x

``` FILE SIZE VM SIZE -------------- -------------- +0.0% +24 +0.0% +24 .text -0.0% -24 [ = ] 0 [Unmapped] [ = ] 0 +0.0% +24 TOTAL ```