Bug 40610: Fix copying of src tarballs

Fixing an issue introduced in 70dc7d9f: var/torbrowser-src was renamed to var/browser-src, but we did not update it in projects/release/build.

Closes #40610 (closed).

requested review from @richard

assigned to @boklm

approved this merge request

merged

also cherry-picked as 288f7d2c to maint-11.5 branch