chore: release spanner 1.26.0 (#4751)

Co-authored-by: Hengfeng Li <hengfeng@google.com>

spanner/CHANGES.md

@@ -1,5 +1,16 @@
 # Changes
 
+## [1.26.0](https://www.github.com/googleapis/google-cloud-go/compare/spanner/v1.25.0...spanner/v1.26.0) (2021-10-11)
+
+
+### Features
+
+* **spanner/spannertest:** implement RowDeletionPolicy in spannertest ([#4961](https://www.github.com/googleapis/google-cloud-go/issues/4961)) ([7800a33](https://www.github.com/googleapis/google-cloud-go/commit/7800a3303b97204a0573780786388437bbbf2673)), refs [#4782](https://www.github.com/googleapis/google-cloud-go/issues/4782)
+* **spanner/spannertest:** Support generated columns ([#4742](https://www.github.com/googleapis/google-cloud-go/issues/4742)) ([324d11d](https://www.github.com/googleapis/google-cloud-go/commit/324d11d3c19ffbd77848c8e19c972b70ff5e9268))
+* **spanner/spansql:** fill in missing hash functions ([#4808](https://www.github.com/googleapis/google-cloud-go/issues/4808)) ([37ee2d9](https://www.github.com/googleapis/google-cloud-go/commit/37ee2d95220efc1aaf0280d0aa2c01ae4b9d4c1b))
+* **spanner/spansql:** support JSON data type ([#4959](https://www.github.com/googleapis/google-cloud-go/issues/4959)) ([e84e408](https://www.github.com/googleapis/google-cloud-go/commit/e84e40830752fc8bc0ccdd869fa7b8fd0c80f306))
+* **spanner/spansql:** Support multiple joins in query ([#4743](https://www.github.com/googleapis/google-cloud-go/issues/4743)) ([81a308e](https://www.github.com/googleapis/google-cloud-go/commit/81a308e909a3ae97504a49fbc9982f7eeb6be80c))
+
 ## [1.25.0](https://www.github.com/googleapis/google-cloud-go/compare/spanner/v1.24.1...spanner/v1.25.0) (2021-08-25)