fix(sveltekit): Only instrument SvelteKit `fetch` if the SDK client is valid #14055

Job	Run time
Get Metadata	12s
Install Dependencies	3m 20s
Check PR branches	3s
Build	1m 28s
Size Check	1m 8s
Lint	4m 31s
Circular Dependency Check	1m 33s
Browser Unit Tests	4m 54s
Upload Artifacts	0s
Node (8) Unit Tests	6m 51s
Node (10) Unit Tests	5m 34s
Node (12) Unit Tests	6m 9s
Node (14) Unit Tests	3m 37s
Node (16) Unit Tests	4m 35s
Node (18) Unit Tests	3m 25s
Node (20) Unit Tests	3m 19s
Playwright (${{ matrix.bundle }}) Tests	0s
Nextjs (Node ${{ matrix.node }}) Tests	0s
Browser Build Tests	53s
Playwright Loader (${{ matrix.bundle }}) Tests	0s
Browser (${{ matrix.browser }}) Tests	0s
Node (${{ matrix.node }}) Integration Tests	0s
E2E Tests (Shard 1)	9m 59s
E2E Tests (Shard 2)	8m 17s
E2E Tests (Shard 3)	7m 6s
Remix (Node ${{ matrix.node }}) Tests	0s
Overhead metrics	0s
All required tests passed or skipped	1s
	1h 16m 55s

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