(all via The Centre for the Study of New Testament Manuscripts)
Then, there’s Tregelles (Luke 22:24, 1 Corinthians 11:16) and Tischendorf (Luke 22:24, 1 Corinthians 11:16), both with φιλονεικία and φιλόνεικος, and a synopsis, via Biblegateway, of Westcott and Hort, Scrivener, and the 2010 SBL Greek New Testament, all with the <ει> spelling in both words. All of the Nestle(-Aland) and UBS editions that I have been able to consult also have φιλονεικία and φιλόνεικος, as does Alexander Souter’s 1916 Oxford edition. The same <ει> spellings are found also in R.G. Tasker’s 1964 Oxford and Cambridge edition of the Greek text translated as The New English Bible of 1961.
It has long been known that the (etymologically) ‘correct’ spelling of the adjective and the abstract noun has <ι>, not <ει>, in contrast to all the printed editions that I have been able to consult. The Greek-English Lexicon of Liddell and Scott, revised and augmented by Jones (LSJ) ‘with the assistance of McKenzie’, explains the situation s.v. φιλόνικος:
the forms φιλόνικος, -νικέω, -νικία and φιλόνεικος, -νεικέω, -νεικία
occur, without any distn. of meaning, e.g. in Isoc. we find περὶ τῶν
καλλίστων ἐφιλονίκησαν 4.85, but τὰς θεὰς περὶ τοῦ κάλλους φιλονεικού-
σας 10.48; μὴ δύσερις ὢν . . , μηδὲ πρὸς πάντας φιλόνικος 1.31; τῆς
πρὸς ἡμᾶς φιλονικίας 4.19, but φιλονεικία in the same sense, 12.158;
φιλόνῑκος is implied by Arist.Rh.1389a12 (where -νεικ-, though
found in good codd., as also in 1363b1, 1368b21, 1370b33, Phgn.
809b35, must be f.l.), καὶ φιλότιμοι μέν εἰσι [οἱ νέοι], μᾶλλον δὲ φιλόνικοι·
ὑπεροχῆς γὰρ ἐπιθυμεῖ ἡ νεότης· ἡ δὲ νίκη ὑπεροχή τις, cf. Poll.
1.178, AB315; the compd. of φιλο- and νεῖκος would be *φιλονεικής;
the sense contentious arises naturally from fond of victory; in SIG
685 (v. φιλονικία sub fin. <Magn. Mae., ii B. C., found in Crete>) we have φιλονικίαν Il.12,36, and φιλονικίᾳ
in OGI335.7 (Pergam., decree of Pitane, ii B. C.); -νῑκ- is also found
in late documents, as POxy.157.1 (vi A. D.).)
The 1959 publication of P.Oxy. XXV 2432 (1st. c. BCE/1st c. CE), which preserves lyric poetry that may be by Simonides, provided further evidence for the <ι> spelling closer in date to the New Testament period. Here’s line 11 from Simonides 541 PMG, ]..ΘΑΛΟΙΤΕ φιλονικίαι: