Shortcodes: Fix warning when attachment src is false in shortcodes module #63383

Job	Run time
detect changed files	8s
Changelogger use	18s
Changelogger validity	37s
Copied files are in sync	8s
Project structure	2m 18s
PHP Compatibility	1m 21s
PHP lint (7.0)	25s
ESLint (non-excluded files only)	0s
PHP Code Sniffer (non-excluded files only)	1m 49s
PHP lint (7.2)	27s
PHP lint (7.4)	32s
PHP Code Sniffer (changes to excluded files only)	0s
PHP lint (8.0)	30s
Check linter exclude lists	0s
PHP lint (8.1)	35s
ESLint (changes to excluded files only)	0s
PHP lint (8.2)	41s
PHP lint (8.3)	36s
Lint GitHub Actions yaml files	0s
Lock files are up to date	0s
Monorepo package version refs	0s
	10m 25s

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