Python ^ semantics wrong (don't match PCRE2)

[NWilson]

Bug Description

Python's meaning of ^ is "start of string, or in /m mode after any newline".
This is different to PCRE2's default meaning for ^, which is "start of string, or in /m mode after newlines which are not the last character in the file".

You are using PCRE2 I believe to emulate Python support? You need to set PCRE2_ALT_CIRCUMFLEX to get behaviour matching Python.

Reproduction steps

1. Switch Regex101 to Python mode, with r"..."gm flags
2. Use the regex ^$
3. Use the text "a<trailing newline>"

Expected Outcome

Python produces one match. Regex101 reports zero matches (same as PCRE2)

Verification:

import re
print( re.search(r"^$", "a\n", re.M) )

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