Cleanup: Add missing license specifiers

Add license specifiers to Go files that were missing them:

```
// SPDX-License-Identifier: GPL-3.0-or-later
```

No functional changes.

cmd/addon-packer/addon-packer.go

@@ -1,5 +1,7 @@
 package main
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"archive/zip"
 	"compress/flate"

cmd/stresser/main.go

@@ -1,5 +1,7 @@
 package main
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"context"
 	"flag"

internal/find_ffmpeg/filenames_nonwindows.go

@@ -2,4 +2,6 @@
 
 package find_ffmpeg
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 const exeSuffix = ""

internal/find_ffmpeg/filenames_windows.go

@@ -2,4 +2,6 @@
 
 package find_ffmpeg
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 const exeSuffix = ".exe"

internal/find_ffmpeg/find_ffmpeg.go

@@ -1,6 +1,8 @@
 // package find_ffmpeg can find an FFmpeg binary on the system.
 package find_ffmpeg
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"context"
 	"errors"

internal/manager/api_impl/dummy/shaman.go

@@ -1,5 +1,7 @@
 package dummy
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"context"
 	"errors"

internal/manager/api_impl/worker_sleep_schedule.go

@@ -1,5 +1,7 @@
 package api_impl
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"errors"
 	"net/http"

internal/manager/persistence/worker_sleep_schedule_test.go

@@ -1,5 +1,7 @@
 package persistence
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"testing"
 	"time"

internal/manager/swagger_ui/swagger_ui.go

@@ -1,5 +1,7 @@
 package swagger_ui
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"embed"
 	"io/fs"

internal/manager/task_state_machine/task_statuses.go

@@ -1,5 +1,7 @@
 package task_state_machine
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import "git.blender.org/flamenco/pkg/api"
 
 var (

internal/manager/task_state_machine/worker_requeue_test.go

@@ -1,5 +1,7 @@
 package task_state_machine
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"testing"
 

internal/own_url/own_url.go

@@ -1,6 +1,8 @@
 // Package own_url provides a way for a process to find a URL on which it can be reached.
 package own_url
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"fmt"
 	"net"

internal/own_url/own_url_test.go

@@ -1,6 +1,8 @@
 // Package own_url provides a way for a process to find a URL on which it can be reached.
 package own_url
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"net"
 	"testing"

internal/stresser/fake_config.go

@@ -1,5 +1,7 @@
 package stresser
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"github.com/rs/zerolog/log"
 

internal/stresser/fake_worker.go

@@ -1,5 +1,7 @@
 package stresser
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"context"
 	"errors"

internal/stresser/stresser.go

@@ -1,5 +1,7 @@
 package stresser
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"context"
 	"fmt"