ci: pip_install.py reason() misses pip's indented ERROR lines #2041

Describe the bug
util/pip_install.py's reason() only matches lines that start with ERROR: . When pip fails building a wheel, it prints the error indented ( ERROR: Failed building wheel for cryptography), so the annotation falls back to pip failed without an ERROR line; see this step's log even though the log does have an ERROR line. Seen on Python pypy3.10 (KTLO) in run 39718608950. The inline shell that reason() replaced (#2031) had the same ^ERROR: gap.

Expected behavior
The annotation names pip's last ERROR: line, ignoring leading whitespace.