test_runner: fix watch cwd with isolation none #7691

Job	Run time
Build slim tarball	1m 17s
aarch64-linux: Cache V8 build	21s
x86_64-darwin: with shared libraries	39m 29s
x86_64-linux: with shared libraries	26m 54s
aarch64-darwin: with shared libraries	26m 0s
aarch64-linux: with shared boringssl-0.20260508.0	22m 38s
aarch64-linux: with shared openssl-1.1.1w	23m 6s
aarch64-linux: with shared openssl-3.6.2	23m 1s
aarch64-linux: with shared openssl-4.0.0	24m 0s
aarch64-linux: with shared openssl-3.5.6	22m 32s
aarch64-linux: with shared openssl-3.0.20	23m 59s
Build slim tarball	1m 17s
x86_64-linux: with shared libraries	26m 54s
aarch64-linux: Cache V8 build	21s
aarch64-darwin: with shared libraries	26m 0s
aarch64-linux: with shared openssl-3.6.2	21m 26s
x86_64-darwin: with shared libraries	39m 29s
aarch64-linux: with shared openssl-1.1.1w	23m 6s
aarch64-linux: with shared boringssl-0.20260508.0	22m 38s
aarch64-linux: with shared openssl-3.0.20	23m 59s
aarch64-linux: with shared openssl-3.5.6	22m 32s
aarch64-linux: with shared openssl-4.0.0	24m 0s
	7h 44m 59s

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