[release] Add 1.61 to interop matrix (#35790)

Post main release `v1.61.0` process

Closes #35790

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35790 from stanley-cheung:release-interop-matrix-update 3667cf06d1
PiperOrigin-RevId: 603743893

tools/interop_matrix/client_matrix.py

@@ -130,6 +130,7 @@ LANG_RELEASE_MATRIX = {
             ("v1.57.0", ReleaseInfo()),
             ("v1.58.0", ReleaseInfo()),
             ("v1.60.0", ReleaseInfo()),
+            ("v1.61.0", ReleaseInfo()),
         ]
     ),
     "go": OrderedDict(
@@ -764,6 +765,12 @@ LANG_RELEASE_MATRIX = {
                     runtimes=["python"], testcases_file="python__master"
                 ),
             ),
+            (
+                "v1.61.0",
+                ReleaseInfo(
+                    runtimes=["python"], testcases_file="python__master"
+                ),
+            ),
         ]
     ),
     "node": OrderedDict(
@@ -858,6 +865,7 @@ LANG_RELEASE_MATRIX = {
             ("v1.57.0", ReleaseInfo()),
             ("v1.58.0", ReleaseInfo()),
             ("v1.60.0", ReleaseInfo()),
+            ("v1.61.0", ReleaseInfo()),
         ]
     ),
     "php": OrderedDict(
@@ -916,6 +924,7 @@ LANG_RELEASE_MATRIX = {
             ("v1.57.0", ReleaseInfo()),
             ("v1.58.0", ReleaseInfo()),
             ("v1.60.0", ReleaseInfo()),
+            ("v1.61.0", ReleaseInfo()),
         ]
     ),
     "csharp": OrderedDict(