It seems the current official version 3.0.3 actually works fine without the RHEL patch as it seems you do can limit connection to TLSv1.2.
As @Chris Kennedy write, you can set the following option in the config-file:
#Options: SSLv3, TLSv1.0, TLSv1.2, HIGH (see man ciphers)
ssl_ciphers=TLSv1.2
WinSCP Client test results:

Set client to Max SSL 3.0:
Connection failed
Set client to Max TLS 1.0:
Connection failed
Set client to Max TLS 1.1
Connection failed
Set client to Max TLS 1.2:
Connection succeed!
Log from WinSCP ver. 5.15.3 with TLS 1.2 connection:
...
. 2020-02-06 15:50:21.774 TLS connect: SSLv3 read server hello A
. 2020-02-06 15:50:21.775 TLS connect: SSLv3 read finished A
. 2020-02-06 15:50:21.775 TLS connect: SSLv3 write change cipher spec A
. 2020-02-06 15:50:21.775 TLS connect: SSLv3 write finished A
. 2020-02-06 15:50:21.775 TLS connect: SSLv3 flush data
. 2020-02-06 15:50:21.775 Using TLSv1.2, cipher TLSv1/SSLv3: ECDHE-RSA-AES256-GCM- SHA384, 2048 bit RSA, ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA Enc=AESGCM(256) Mac=AEAD
. 2020-02-06 15:50:21.775 TLS connection established
I did also play around with the other TLSv1.2, TLSv1.0, SSLv3 option-values, and they seem to be respected.