Update to go 1.20 (#3609)

Release notes: https://tip.golang.org/doc/go1.20

Changes required:

- Updated `go.mod` - this also controls what CI uses
- `rand` is now automatically seeded

---

#### Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No

#### Type of change

<!--- Please check the type of change your PR introduces: --->
- [ ] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [x] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* #3568 

#### Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [x] 💚 E2E

src/go.mod

@@ -1,6 +1,6 @@
 module github.com/alcionai/corso/src
 
-go 1.19
+go 1.20
 
 replace github.com/kopia/kopia => github.com/alcionai/kopia v0.12.2-0.20230502235504-2509b1d72a79
 

src/internal/m365/exchange/mock/collections.go

@@ -89,8 +89,6 @@ func NewContactCollection(pathRepresentation path.Path, numMessagesToReturn int)
 		Names:        []string{},
 	}
 
-	rand.Seed(time.Now().UnixNano())
-
 	middleNames := []string{
 		"Argon",
 		"Bernard",