Fix brittle POSIX ManualCommand progress-line assertion in NativeCliInstallerTests #1996

Summary

NativeCliInstallerTests.GetInstallCommand_RemoteBootstrapsEmitProgressLinesInStageOrder fails on current v3-beta even with no local changes. Production output is correct; the assertion is wrong.

Discovered while working on #1994 (launcher → dispatcher rename). Confirmed unrelated: the same failure reproduces on a clean origin/v3-beta tree with that PR's changes stashed. Left out of #1994 on purpose so the rename PR stayed a single concern.

Root cause

• Packages/src/Editor/Infrastructure/CLI/NativeCliCommandBuilder.cs still emits echo 'Downloading installer script...' (and the verify/start lines) in the POSIX remote install script.
• POSIX ManualCommand is wrapped via BuildLoginShellPosixInstallScriptCommand.
• That wrap escapes inner single quotes through QuotePosixShellValue, so ManualCommand contains an escaped form such as echo '"'"'Downloading installer script...' rather than the bare echo 'Downloading installer script...'.
• The test's IndexOf("echo 'Downloading installer script...'") therefore returns -1.
• Windows passes because its ManualCommand is not login-shell-wrapped, so no quote escaping is inserted. That also explains why the Windows-only asserts around the same progress lines stay green.

Suggested fix

Fix the test, not production strings:

1. Assert against the pre-wrap POSIX command string, or
2. Escape the expected substring with the same QuotePosixShellValue rules before matching against ManualCommand.

Do not change the production echo / Write-Output progress text just to satisfy the brittle assertion. User-visible behavior is already correct; Unity progress labels consume those installer progress lines as intended.

Evidence

• Suite result under fix: Rename the global uloop launcher to dispatcher in user-facing text #1994 verification: NativeCliInstallerTests 32 / 33 passed; only this case failed.
• Same failure on clean origin/v3-beta with the rename changes stashed.