Increase private key length

[hv-singh]

Add some more characters to the private key. We're updating the GCP service account regex and the new pattern requires at least 64 characters after the -----BEGIN pem block header.

Why 64?
The purpose is to filter out trivially short content between -----BEGIN and -----END that isn't a real key. A real private key has a substantial base64-encoded body:

• RSA 2048-bit (most common for GCP): ~1,680 characters
• RSA 4096-bit: ~3,240 characters
• EC P-256 (smallest viable): ~160 characters