Bumping Abseil version to latest LTS (#10433)

* Bumping Abseil version to latest LTS

* Upgrade PHP build to latest docker image

* Deleting php 7.0 kokoro build now that it's not supported

* Putting old PHP test back

* Fix test cases that exceed PHP_INT_MAX

protobuf_deps.bzl

diff --git a/protobuf_deps.bzl b/protobuf_deps.bzl
index 4a2d791..e276c88 100644
--- a/protobuf_deps.bzl
+++ b/protobuf_deps.bzl
@@ -41,8 +41,8 @@
         _github_archive(
             name = "com_google_absl",
             repo = "https://github.com/abseil/abseil-cpp",
-            commit = "215105818dfde3174fe799600bb0f3cae233d0bf",
-            sha256 = "b4e20d9e752a75c10636675691b1e9c2698e0764cb404987d0ffa77223041c19",
+            commit = "273292d1cfc0a94a65082ee350509af1d113344d",
+            sha256 = "6764f226bd6e2d8ab9fe2f3cab5f45fb1a4a15c04b58b87ba7fa87456054f98b",
         )
 
     if not native.existing_rule("zlib"):