[NFC] CRM_Extension_Manager_ModuleUpgTest - use ?? instead of error-suppression operator

[demeritcowboy]

Overview

This is the same as #21206 but in another file.

Can potentially cause problems in php 8 with certain error handlers.
Note also that assertEquals() treats 0 and null as equal, so have tightened it up by using assertSame.
Addresses test fails in #21064:

not ok 1930 - Error: CRM_Extension_Manager_ModuleUpgTest::testInstallDisableUninstall
not ok 1931 - Failure: CRM_Extension_Manager_ModuleUpgTest::testInstallDisableEnable
  ---
  message: Failed asserting that true matches expected false.
  severity: fail
  data:
    got: true
    expected: false
  ...
  not ok 1932 - Error: CRM_Extension_Manager_ModuleUpgTest::testInstall_DirtyRemove_Disable_Uninstall
not ok 1933 - Error: CRM_Extension_Manager_ModuleUpgTest::testInstall_DirtyRemove_Disable_Restore

[civibot]

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