Hebrews 1:8 is not a teaching on the trinity or that we should believe or confess that Jesus is God. Hebrews is saying your throne oh God is forever. Not Jesus is forever. In Hebrews it's quoted referring to Jesus having the use of that throne.
Hebrews 1:8
But unto the Son he saith, Thy throne, O God, is for ever and ever: a sceptre of righteousness is the sceptre of thy kingdom.
Psalms 45:6
Thy throne, O God, is for ever and ever: the sceptre of thy kingdom is a right sceptre.
“Your throne is God.” Hebrews 1:8 is an almost exact quotation from the Septuagint version of Psalm 45:6, which itself was a very good translation of the Hebrew text of Psalm 45:6, and Hebrews 1:9 is from the Septuagint of Psalm 45:7. The theme of Hebrews 1 centers around the Father’s rule and elevation of the Son over the rest of creation. God spoke through the prophets, and then through His Son, who He appointed heir of all things and who is now seated at God’s right hand as second in command under God.
The God of the Son—anointed him and set him above his companions, such that the Son now sits on God’s right hand. Hebrews exalts the Son, and in so doing exalts the Father. But in contrast to what Trinitarians say, Hebrews 1:8 (and thus Psalm 45:6) does not call Jesus “God” and does not support the Trinity. To see that fully, one must study Psalm 45. Upon examination, Psalm 45 does not support the Trinity, so when it is quoted in Hebrews 1:8 then that quotation does not support the Trinity either. The Jews read Psalm 45 for centuries and never concluded that the Messiah would be “God in the flesh” or somehow be part of a Triune God.