Fix homotopy lambda spell check (#4726)

Move the LambaEulerHeun exception to an identifier allow-list so the normal lambda/LAMBDA spelling introduced by the homotopy operator is no longer treated as a misspelling.

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>

Author: ChrisRackauckas-Claude

.typos.toml

@@ -1,3 +1,6 @@
+[default.extend-identifiers]
+LambaEulerHeun = "LambaEulerHeun"
+
 [default.extend-words]
 nin = "nin"
 nd = "nd"
@@ -13,5 +16,4 @@ fo = "fo"
 shs = "shs"
 setp = "setp"
 CMO = "CMO"
-Lambda = "Lamba"
 gam = "gam"