Tests: error report corrected for unknown variables in "response_headers"

[andrey-zelenkov]

For more information please see #1191

[andrey-zelenkov]

Rebased.

% git range-diff 35adeb6d...3bcf4993
-:  -------- > 1:  d494d2eb Wasm-wc: Bump the h2 crate from 0.4.2 to 0.4.4
-:  -------- > 2:  e6d8fc66 njs (lowercase) is more preferred way to mention
-:  -------- > 3:  6e79da47 Docs: njs (lowercase) is more preferred way to mention
-:  -------- > 4:  5f606742 Tests: added $request_uri tests with proxy
-:  -------- > 5:  a625a0b1 Tests: compatibility with OpenSSL 3.2.0
-:  -------- > 6:  2d7a8468 HTTP: Added variable validation to the response_headers option
1:  35adeb6d = 7:  3bcf4993 Tests: error report corrected for unknown variables in "response_headers"