Fix deprecation of variable expansion

[christianlupus]

Topic and Scope

The variable expansion in the form of "${varName}" in PHP is deprecated. Instead, one uses "{$varName}". The tests have the old syntax and should be fixed.

Concerns/issues

None

Formal requirements

There are some formal requirements that should be satisfied. Please mark those by checking the corresponding box.

• I did check that the app can still be opened and does not throw any browser logs
• I created tests for newly added PHP code (check this if no PHP changes were made)
• I updated the OpenAPI specs and added an entry to the API changelog (check if API was not modified)
• I notified the matrix channel if I introduced an API change

[github-actions]

Test Results

   12 files    572 suites   1m 32s ⏱️
  552 tests   552 ✅ 0 💤 0 ❌
2 208 runs  2 207 ✅ 1 💤 0 ❌

Results for commit add0007.

[christianlupus]

/approve

[nextcloud-cookbook-bot]

Automatically approved by GitHub action on behalf of /approve