Fix defaultInterpreterPath variable expansion and stabilize interpret… #458

Job	Run time
Create VSIX	33s
Lint	17s
TypeScript Unit Tests (ubuntu-latest)	40s
TypeScript Unit Tests (windows-latest)	1m 35s
Smoke Tests (ubuntu-latest, 3.9)	2m 20s
Smoke Tests (windows-latest, 3.12)	3m 49s
Smoke Tests (ubuntu-latest, 3.12)	2m 13s
Smoke Tests (macos-latest, 3.14)	2m 12s
Smoke Tests (macos-latest, 3.9)	3m 8s
Smoke Tests (windows-latest, 3.14)	2m 48s
Smoke Tests (ubuntu-latest, 3.14)	2m 14s
Smoke Tests (windows-latest, 3.9)	3m 41s
Smoke Tests (macos-latest, 3.12)	2m 14s
E2E Tests	0s
Integration Tests	0s
	27m 44s

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