patch 8.2.2182: Vim9: value of 'magic' is still relevant

Problem:    Vim9: value of 'magic' is still relevant.
Solution:   Always behave like 'magic' is on in Vim9 script (closes #7509)
diff --git a/src/buffer.c b/src/buffer.c
index 8497bcf..b3889b7 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2605,7 +2605,7 @@
 		p = pat;
 		if (*p == '^' && !(attempt & 1))	 // add/remove '^'
 		    ++p;
-		regmatch.regprog = vim_regcomp(p, p_magic ? RE_MAGIC : 0);
+		regmatch.regprog = vim_regcomp(p, magic_isset() ? RE_MAGIC : 0);
 		if (regmatch.regprog == NULL)
 		{
 		    vim_free(pat);