Fix wasm32 build by gating MultiFileSession on non-wasm targets #32611

Job	Run time
Python (test)	38s
C/C++ (lint)	7s
lint-toml	6s
Check build with minimal dependencies	46s
Python (lint)	40s
C++ build	38s
validate-workflow-yaml	6s
Java	36s
WASM integration smoke test	1m 13s
C API test build	31s
License Check and Audit Check (bans licenses sources)	49s
License Check and Audit Check (advisories)	51s
Check generated source files are up to date	44s
Rust build (all-features)	47s
Rust (lint, no default)	45s
Rust build (default features)	35s
Rust build (wasm32 with default features)	34s
Rust build (with tokio dispatcher)	40s
Mirror DuckDB to R2 / Resolve DuckDB version and check R2	5s
DuckDB libraries available in R2	4s
Mirror DuckDB to R2 / Mirror DuckDB ${{ matrix.archive }} to R2	0s
Rust (docs)	28s
Rust tests (linux-arm64)	27s
SQL logic tests	27s
Rust (lint)	28s
Rust tests (windows-x64)	34s
	13m 39s

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