Installers of TortoiseSVN are digitally signed, so AFAIK if the correct signature is present and is valid, then the installer file is authentic (i.e., hasn't been modified).
You can check the digital signature in the installer file's Properties, as shown on the screenshot.
Get-AuthenticodeSignature .\TortoiseSVN-1.14.5.29465-x64-svn-1.14.2.msi | Format-List
SignerCertificate : [Subject]
E=torto...@gmail.com, CN="Open Source Developer, Stefan KUENG", O=Open Source Developer,
L=Altstätten, C=CH
[Issuer]
CN=Certum Code Signing 2021 CA, O=Asseco Data Systems S.A., C=PL
[Serial Number]
157F6D9D452A2AE334CA4348D1E265F0
[Not Before]
12-May-22 10:51:00
[Not After]
12-May-23 10:50:59
[Thumbprint]
D1BB43B9FD69918D2E288BF74394BC86D32B1646
TimeStamperCertificate : [Subject]
CN=Certum Timestamp 2022, O=Asseco Data Systems S.A., C=PL
[Issuer]
CN=Certum Timestamping 2021 CA, O=Asseco Data Systems S.A., C=PL
[Serial Number]
2BD4AE70B9D0635B2AE984C8D674AA30
[Not Before]
28-Jul-22 11:56:26
[Not After]
27-Jul-33 11:56:26
[Thumbprint]
BF4F6BC4982DDE1505A8EFC8C7A79D4D143500CE
Status : Valid
StatusMessage : Signature verified.
Path : C:\MyDownloads\TortoiseSVN-1.14.5.29465-x64-svn-1.14.2.msi
SignatureType : Authenticode
IsOSBinary : False