Update tests/presubmit.sh with modern syntax for Fuchsia bugs
Update tests/presubmit.sh with modern syntax for Fuchsia bugs

Replaces "fxb/#" with the Monorail syntax "fuchsia:#".
This updates https://swiftshader-review.googlesource.com/c/SwiftShader/+/44129.

Bug: None
Change-Id: I9dc0e617cdec2d1a8b980ee7aca2c718ce4021d6
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/46328
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Tested-by: David Dorwin <7285fc8420ade15dc45c0d23efd2156d30510c16@google.com>

bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader